/* ==========================================================================
   introtoalgo — site.css (the only stylesheet)
   Sections: tokens · base · layout · header/footer · buttons · home ·
   roadmap · lesson · components · practice list · workspace · archive · misc
   ========================================================================== */

/* ---------- tokens ---------- */
:root {
  --font-ui: "Bricolage Grotesque", ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-read: "Source Serif 4", "Iowan Old Style", Charter, "Palatino Linotype", Georgia, serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;

  --bg: #f6f5f0;
  --bg-2: #eeede6;
  --surface: #ffffff;
  --surface-2: #f3f2ec;
  --line: #e2e0d6;
  --line-2: #c8c5b7;
  --fg: #191a16;
  --fg-2: #46473f;
  --fg-3: #6a6a61;

  --algo: #46710f;
  --algo-fill: #3d6410;
  --algo-soft: #eaf3d5;
  --prac: #9a4b00;
  --prac-fill: #8f4500;
  --prac-soft: #fbecd7;
  --ai: #6b3fd0;
  --ai-fill: #6237c4;
  --ai-soft: #eee8fc;
  --on-fill: #ffffff;

  --good: #1d7a3e;
  --good-soft: #e1f2e6;
  --bad: #b3261e;
  --bad-soft: #fbe6e3;
  --info: #1d5fb8;
  --info-soft: #e4eefb;
  --warn: #8a5700;

  --code-bg: #f1f0e9;
  --code-line: #e3e1d6;
  --tk-k: #8b2fb3;
  --tk-s: #2f7a1f;
  --tk-n: #b25000;
  --tk-c: #66665c;
  --tk-f: #1d5fb8;
  --tk-l: #b3261e;
  --tk-b: #0b7285;
  --tk-t: #9a4b00;
  --tk-o: #55564d;
  --tk-p: #1d5fb8;

  --shadow: 0 1px 2px rgba(25, 26, 22, 0.05), 0 4px 16px rgba(25, 26, 22, 0.05);
  --radius: 10px;
  --radius-sm: 6px;
  --header-h: 60px;
  --wrap: 1180px;
  --read: 40rem;
  --tap: 40px;

  --accent: var(--algo);
  --accent-fill: var(--algo-fill);
  --accent-soft: var(--algo-soft);
  color-scheme: light;
}

@media (pointer: coarse) { :root { --tap: 44px; } }

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0e0f0c; --bg-2: #13140f; --surface: #161712; --surface-2: #1d1e18; --line: #2a2b24; --line-2: #3d3e35;
    --fg: #edece4; --fg-2: #b8b7ab; --fg-3: #8f8e83;
    --algo: #c8f047; --algo-fill: #c8f047; --algo-soft: rgba(200, 240, 71, 0.1);
    --prac: #ffb54d; --prac-fill: #ffb54d; --prac-soft: rgba(255, 181, 77, 0.1);
    --ai: #bba6ff; --ai-fill: #bba6ff; --ai-soft: rgba(187, 166, 255, 0.11);
    --on-fill: #0e0f0c;
    --good: #6fdc8c; --good-soft: rgba(111, 220, 140, 0.1); --bad: #ff8b7d; --bad-soft: rgba(255, 139, 125, 0.1);
    --info: #7cc4ff; --info-soft: rgba(124, 196, 255, 0.1); --warn: #ffcf6b;
    --code-bg: #121310; --code-line: #24251f;
    --tk-k: #c9a8ff; --tk-s: #b5e48c; --tk-n: #ffb86b; --tk-c: #7f8075; --tk-f: #7cc4ff; --tk-l: #ff8b7d; --tk-b: #67e0f0; --tk-t: #ffcf8b; --tk-o: #a9a89c; --tk-p: #7cc4ff;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.25);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0e0f0c; --bg-2: #13140f; --surface: #161712; --surface-2: #1d1e18; --line: #2a2b24; --line-2: #3d3e35;
  --fg: #edece4; --fg-2: #b8b7ab; --fg-3: #8f8e83;
  --algo: #c8f047; --algo-fill: #c8f047; --algo-soft: rgba(200, 240, 71, 0.1);
  --prac: #ffb54d; --prac-fill: #ffb54d; --prac-soft: rgba(255, 181, 77, 0.1);
  --ai: #bba6ff; --ai-fill: #bba6ff; --ai-soft: rgba(187, 166, 255, 0.11);
  --on-fill: #0e0f0c;
  --good: #6fdc8c; --good-soft: rgba(111, 220, 140, 0.1); --bad: #ff8b7d; --bad-soft: rgba(255, 139, 125, 0.1);
  --info: #7cc4ff; --info-soft: rgba(124, 196, 255, 0.1); --warn: #ffcf6b;
  --code-bg: #121310; --code-line: #24251f;
  --tk-k: #c9a8ff; --tk-s: #b5e48c; --tk-n: #ffb86b; --tk-c: #7f8075; --tk-f: #7cc4ff; --tk-l: #ff8b7d; --tk-b: #67e0f0; --tk-t: #ffcf8b; --tk-o: #a9a89c; --tk-p: #7cc4ff;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.25);
  color-scheme: dark;
}

/* per-track accent */
[data-track="practice"] { --accent: var(--prac); --accent-fill: var(--prac-fill); --accent-soft: var(--prac-soft); }
[data-track="ai"] { --accent: var(--ai); --accent-fill: var(--ai-fill); --accent-soft: var(--ai-soft); }
.t-algo { --accent: var(--algo); --accent-fill: var(--algo-fill); --accent-soft: var(--algo-soft); }
.t-prac { --accent: var(--prac); --accent-fill: var(--prac-fill); --accent-soft: var(--prac-soft); }
.t-ai { --accent: var(--ai); --accent-fill: var(--ai-fill); --accent-soft: var(--ai-soft); }

/* ---------- base ---------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; text-size-adjust: 100%; scroll-padding-top: calc(var(--header-h) + 16px); }
@media (prefers-reduced-motion: no-preference) { html { scroll-behavior: smooth; } }
body {
  margin: 0; min-height: 100vh; display: flex; flex-direction: column;
  background: var(--bg); color: var(--fg);
  font-family: var(--font-ui); font-size: 1rem; line-height: 1.55;
  -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}
main { flex: 1 0 auto; outline: none; }
img, svg { max-width: 100%; }
img { height: auto; }
a { color: inherit; }
h1, h2, h3, h4 { line-height: 1.2; margin: 0; font-weight: 700; letter-spacing: -0.015em; text-wrap: balance; }
p, li { text-wrap: pretty; }
p { margin: 0; }
button, input, select, textarea { font: inherit; color: inherit; }
button { cursor: pointer; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 3px; }
::selection { background: var(--accent-soft); color: var(--fg); }
code, kbd, pre, textarea, .cm-editor { font-family: var(--font-mono); font-variant-ligatures: none; }
kbd { font-size: 0.75em; border: 1px solid var(--line-2); border-bottom-width: 2px; border-radius: 4px; padding: 0.05em 0.35em; background: var(--surface); }
.icon { width: 1.15em; height: 1.15em; flex: none; vertical-align: -0.2em; }
.sr-only { position: absolute !important; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0; }
.muted { color: var(--fg-3); }
[hidden] { display: none !important; }

.skip-link { position: absolute; left: 12px; top: -48px; z-index: 100; background: var(--accent-fill); color: var(--on-fill); padding: 8px 14px; border-radius: var(--radius-sm); font-weight: 600; text-decoration: none; }
.skip-link:focus { top: 10px; }

.wrap { width: 100%; max-width: var(--wrap); margin: 0 auto; padding: 0 16px; }
@media (min-width: 720px) { .wrap { padding: 0 28px; } }
.wrap--narrow { max-width: 820px; }
.wrap--narrow .prose { max-width: var(--read); }

.eyebrow { display: inline-flex; align-items: center; gap: 0.5em; font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--accent); font-weight: 500; }
.section-label { font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--fg-3); font-weight: 500; margin-bottom: 12px; }
.section-title { font-size: clamp(1.4rem, 2.6vw, 1.9rem); letter-spacing: -0.025em; font-weight: 750; }
.tag { display: inline-flex; align-items: center; font-family: var(--font-mono); font-size: 0.72rem; padding: 0.15em 0.55em; border-radius: 99px; border: 1px solid var(--line-2); color: var(--fg-2); white-space: nowrap; }
.soon { font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.04em; text-transform: uppercase; color: var(--fg-3); border: 1px dashed var(--line-2); padding: 0.05em 0.45em; border-radius: 4px; white-space: nowrap; }
.chip { display: inline-flex; align-items: center; gap: 0.4em; padding: 0.3em 0.75em; border-radius: 99px; background: var(--surface); border: 1px solid var(--line); text-decoration: none; font-size: 0.9rem; }
a.chip:hover { border-color: var(--accent); color: var(--accent); }
.chip--soon { color: var(--fg-3); }

/* ---------- header ---------- */
.site-header { position: sticky; top: 0; z-index: 50; background: color-mix(in srgb, var(--bg) 88%, transparent); backdrop-filter: saturate(1.4) blur(10px); -webkit-backdrop-filter: saturate(1.4) blur(10px); border-bottom: 1px solid var(--line); }
.site-header__inner { max-width: var(--wrap); margin: 0 auto; padding: 0 16px; height: var(--header-h); display: flex; align-items: center; gap: 12px; }
@media (min-width: 720px) { .site-header__inner { padding: 0 28px; gap: 24px; } }
.is-workspace .site-header__inner { max-width: none; }
.logo { display: inline-flex; align-items: center; min-height: var(--tap); min-width: var(--tap); gap: 0.4em; font-family: var(--font-mono); font-weight: 700; font-size: 1.05rem; text-decoration: none; letter-spacing: -0.02em; white-space: nowrap; }
.logo__prompt { color: var(--algo); font-weight: 500; }
.logo--small { font-size: 0.95rem; }
.site-nav { display: flex; gap: 2px; margin-left: auto; }
.site-nav__link { position: relative; display: inline-flex; align-items: center; justify-content: center; min-height: var(--tap); min-width: var(--tap); padding: 0 12px; border-radius: 8px; text-decoration: none; font-weight: 550; font-size: 0.95rem; color: var(--fg-2); transition: color 0.15s, background 0.15s; }
.site-nav__link:hover { color: var(--fg); background: var(--surface-2); }
.site-nav__link[aria-current="page"] { color: var(--fg); }
.site-nav__link[aria-current="page"]::after { content: ""; position: absolute; left: 12px; right: 12px; bottom: calc((var(--tap) - var(--header-h)) / 2); height: 2px; border-radius: 2px; background: var(--accent); }
.site-nav__link--algorithms[aria-current] { --accent: var(--algo); }
.site-nav__link--practice[aria-current] { --accent: var(--prac); }
.site-nav__link--ai[aria-current] { --accent: var(--ai); }
.theme-toggle { display: inline-grid; place-items: center; width: var(--tap); height: var(--tap); border-radius: 8px; border: 1px solid var(--line); background: var(--surface); color: var(--fg-2); }
.theme-toggle:hover { color: var(--fg); border-color: var(--line-2); }
.theme-toggle .icon { width: 18px; height: 18px; }
.theme-toggle__moon { display: none; }
:root[data-theme="dark"] .theme-toggle__sun { display: none; }
:root[data-theme="dark"] .theme-toggle__moon { display: block; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .theme-toggle__sun { display: none; }
  :root:not([data-theme="light"]) .theme-toggle__moon { display: block; }
}
@media (max-width: 560px) {
  .logo__name { display: none; }
  .site-nav { margin-left: 0; flex: 1; justify-content: center; }
  .site-nav__link { padding: 0 9px; font-size: 0.92rem; }
  .site-nav__link[aria-current="page"]::after { left: 9px; right: 9px; }
}

/* ---------- footer ---------- */
.site-footer { border-top: 1px solid var(--line); margin-top: 80px; background: var(--bg-2); }
.is-workspace .site-footer { display: none; }
.site-footer__inner { max-width: var(--wrap); margin: 0 auto; padding: 40px 16px 24px; display: grid; gap: 32px; }
@media (min-width: 720px) { .site-footer__inner { grid-template-columns: 1.3fr 1fr; padding: 48px 28px 28px; } }
.site-footer__brand p { color: var(--fg-3); margin-top: 10px; max-width: 34ch; font-size: 0.95rem; }
.site-footer__nav { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; }
.site-footer__nav h2 { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--fg-3); font-weight: 500; margin-bottom: 10px; }
.site-footer__nav a { display: flex; align-items: center; min-height: var(--tap); text-decoration: none; color: var(--fg-2); }
.site-footer__nav a:hover { color: var(--fg); text-decoration: underline; }
.site-footer__base { max-width: var(--wrap); margin: 0 auto; padding: 16px; display: flex; justify-content: space-between; flex-wrap: wrap; gap: 8px; border-top: 1px solid var(--line); font-family: var(--font-mono); font-size: 0.75rem; color: var(--fg-3); }
@media (min-width: 720px) { .site-footer__base { padding: 18px 28px; } }

/* ---------- buttons ---------- */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 0.5em; min-height: 40px; padding: 0.5em 1.05em; border-radius: 8px; border: 1px solid transparent; font-weight: 600; font-size: 0.95rem; text-decoration: none; line-height: 1.2; transition: background 0.15s, border-color 0.15s, color 0.15s, transform 0.1s; white-space: nowrap; }
.btn:active { transform: translateY(1px); }
.btn--accent { background: var(--accent-fill); color: var(--on-fill); }
.btn--accent:hover { filter: brightness(1.08); }
.btn--ghost { background: var(--surface); border-color: var(--line-2); color: var(--fg); }
.btn--ghost:hover { border-color: var(--accent); color: var(--accent); }
.btn--lg { min-height: 48px; padding: 0.65em 1.3em; font-size: 1.02rem; }
.btn--sm { min-height: max(36px, calc(var(--tap) - 4px)); padding: 0.35em 0.8em; font-size: 0.88rem; }
.btn[disabled], .btn-icon[disabled] { opacity: 0.45; cursor: not-allowed; }
.btn-icon { display: inline-grid; place-items: center; width: var(--tap); height: var(--tap); border-radius: 8px; border: 1px solid var(--line); background: var(--surface); color: var(--fg-2); }
.btn-icon:hover { color: var(--fg); border-color: var(--line-2); }
.btn-text { background: none; border: 0; padding: 0 4px; min-height: var(--tap); color: var(--fg-2); text-decoration: underline; text-underline-offset: 3px; font-size: 0.92rem; }
.btn-text:hover { color: var(--fg); }

/* progress bars */
.bar { display: block; position: relative; height: 6px; border-radius: 99px; background: var(--line); overflow: hidden; }
.bar__fill { position: absolute; inset: 0 auto 0 0; background: var(--accent); border-radius: 99px; transition: width 0.4s ease; }
.bar--easy { --accent: var(--good); }
.bar--medium { --accent: var(--warn); }
.bar--hard { --accent: var(--bad); }

/* ---------- home ---------- */
.hero { display: grid; gap: 40px; padding: 56px 0 40px; align-items: center; }
@media (min-width: 980px) { .hero { grid-template-columns: 1.05fr 1fr; gap: 56px; padding: 88px 0 64px; } }
.hero__title { font-size: clamp(2.3rem, 5.6vw, 4rem); line-height: 1.02; letter-spacing: -0.04em; font-weight: 800; margin: 18px 0 20px; }
.hero__hl { color: var(--algo); display: block; }
:root:not([data-theme="dark"]) .hero__hl { color: var(--algo); }
.hero__lead { font-size: clamp(1.05rem, 1.6vw, 1.2rem); color: var(--fg-2); max-width: 36rem; }
.hero__cta { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 28px; }
.hero__demo { min-width: 0; }
.hero__demo .tracer { margin: 0; box-shadow: var(--shadow); }

.continue { margin: 8px 0 40px; }
.continue__list { list-style: none; margin: 0; padding: 0; display: grid; gap: 12px; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); }
.continue__item { display: flex; flex-direction: column; gap: 4px; padding: 14px 16px; border: 1px solid var(--line); border-left: 3px solid var(--accent); border-radius: var(--radius); background: var(--surface); text-decoration: none; }
.continue__item:hover { border-color: var(--accent); }
.continue__kind { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--accent); }
.continue__title { font-weight: 650; }

.doors { display: grid; gap: 16px; margin: 0 0 72px; }
@media (min-width: 860px) { .doors { grid-template-columns: repeat(3, 1fr); gap: 20px; } }
.door { --accent: var(--algo); --accent-soft: var(--algo-soft); position: relative; display: flex; flex-direction: column; gap: 12px; padding: 26px 24px 22px; border-radius: 14px; background: var(--surface); border: 1px solid var(--line); text-decoration: none; overflow: hidden; transition: border-color 0.2s, transform 0.2s, box-shadow 0.2s; }
.door::before { content: ""; position: absolute; inset: 0 0 auto 0; height: 4px; background: var(--accent); }
.door:hover { border-color: var(--accent); box-shadow: var(--shadow); }
@media (prefers-reduced-motion: no-preference) { .door:hover { transform: translateY(-2px); } }
.door--practice { --accent: var(--prac); --accent-soft: var(--prac-soft); }
.door--ai { --accent: var(--ai); --accent-soft: var(--ai-soft); }
.door__icon { display: inline-grid; place-items: center; width: 44px; height: 44px; border-radius: 10px; background: var(--accent-soft); color: var(--accent); }
.door__icon .icon { width: 24px; height: 24px; }
.door__title { font-size: 1.6rem; font-weight: 800; letter-spacing: -0.03em; }
.door__text { color: var(--fg-2); }
.door__points { list-style: none; padding: 0; margin: 0; display: grid; gap: 6px; font-size: 0.92rem; color: var(--fg-2); }
.door__points li { display: flex; gap: 8px; }
.door__points li::before { content: ""; flex: none; width: 6px; height: 6px; margin-top: 0.55em; border-radius: 2px; background: var(--accent); }
.door__foot { margin-top: auto; padding-top: 10px; display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.door__stat { font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); }
.door__go { color: var(--accent); }
.door__bar { margin-top: 2px; }
@media (min-width: 600px) and (max-width: 859px) {
  .door { display: grid; grid-template-columns: 1.15fr 1fr; column-gap: 28px; row-gap: 10px; align-items: start; }
  .door > * { grid-column: 1; }
  .door > .door__points { grid-column: 2; grid-row: 1 / span 3; align-self: center; }
  .door > .door__foot, .door > .door__bar { grid-column: 1 / -1; }
}

.start { display: grid; gap: 28px; margin-bottom: 72px; }
@media (min-width: 900px) { .start { grid-template-columns: 0.8fr 1.2fr; gap: 48px; align-items: start; } }
.start__intro p { color: var(--fg-2); margin-top: 12px; max-width: 34rem; }
.path { list-style: none; margin: 0; padding: 0; display: grid; gap: 10px; counter-reset: p; }
.path__item { display: flex; align-items: flex-start; gap: 16px; padding: 14px 16px; border-radius: var(--radius); border: 1px solid var(--line); background: var(--surface); text-decoration: none; }
a.path__item:hover { border-color: var(--accent); }
.path__item.is-soon { opacity: 0.7; }
.path__n { flex: none; display: grid; place-items: center; width: 30px; height: 30px; border-radius: 50%; border: 1.5px solid var(--accent); color: var(--accent); font-family: var(--font-mono); font-weight: 700; font-size: 0.85rem; }
.path__body { display: flex; flex-direction: column; gap: 2px; min-width: 0; flex: 1; }
.path__kind { font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); }
.path__title { font-weight: 650; font-size: 1.05rem; }
.path__note { color: var(--fg-2); font-size: 0.93rem; }

.how { margin-bottom: 56px; }
.how__grid { display: grid; gap: 16px; margin-top: 20px; }
@media (min-width: 820px) { .how__grid { grid-template-columns: repeat(3, 1fr); gap: 24px; } }
.how__item { padding: 20px 0 0; border-top: 2px solid var(--line); }
.how__item .icon { width: 26px; height: 26px; color: var(--accent); }
.how__item h3 { margin: 10px 0 6px; font-size: 1.1rem; }
.how__item p { color: var(--fg-2); }
.archive-teaser { border: 1px dashed var(--line-2); border-radius: var(--radius); padding: 16px 18px; color: var(--fg-2); }
.archive-teaser p .icon { margin-right: 8px; color: var(--fg-3); }
.archive-teaser a { color: var(--accent); }

/* ---------- page hero (roadmaps, practice, about) ---------- */
.page-hero { padding: 48px 0 32px; }
@media (min-width: 720px) { .page-hero { padding: 64px 0 40px; } }
.page-hero__title { font-size: clamp(2rem, 4.6vw, 3.2rem); letter-spacing: -0.035em; font-weight: 800; margin: 14px 0 14px; line-height: 1.05; }
.page-hero__lead { font-size: 1.12rem; color: var(--fg-2); max-width: 44rem; }
.progress-block { margin-top: 28px; padding: 18px 20px; border: 1px solid var(--line); border-radius: 12px; background: var(--surface); max-width: 44rem; }
.progress-block__row { display: flex; justify-content: space-between; flex-wrap: wrap; gap: 6px 16px; margin-bottom: 10px; font-size: 0.95rem; }
.progress-block__cta { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 16px; }
.progress-block__cta .btn { white-space: normal; text-align: left; }
.order-note { display: flex; gap: 12px; margin-top: 18px; max-width: 44rem; color: var(--fg-2); font-size: 0.95rem; }
.order-note .icon { color: var(--accent); margin-top: 0.2em; }

/* ---------- roadmap ---------- */
.rm-index { margin-top: 28px; max-width: 44rem; }
.rm-index__list { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 200px), 1fr)); gap: 0 20px; }
.rm-index__link { display: flex; align-items: center; gap: 10px; min-height: var(--tap); padding: 2px 0; text-decoration: none; color: var(--fg-2); font-size: 0.93rem; border-bottom: 1px solid var(--line); }
.rm-index__link:hover { color: var(--accent); }
.rm-index__n { flex: none; width: 1.8em; font-family: var(--font-mono); font-size: 0.78rem; color: var(--accent); font-weight: 700; }
.rm-index__name { flex: 1; min-width: 0; }
.rm-index__count { font-family: var(--font-mono); font-size: 0.72rem; color: var(--fg-3); }
.roadmap { list-style: none; margin: 16px 0 0; padding: 0; }
.rm-module { display: grid; grid-template-columns: 44px 1fr; gap: 16px; }
@media (min-width: 720px) { .rm-module { grid-template-columns: 56px 1fr; gap: 24px; } }
.rm-module__rail { position: relative; display: flex; justify-content: center; }
.rm-module__rail::before { content: ""; position: absolute; top: 0; bottom: 0; width: 2px; background: var(--line); }
.rm-module:first-child .rm-module__rail::before { top: 22px; }
.rm-module:last-child .rm-module__rail::before { bottom: auto; height: 22px; }
.rm-module__num { position: relative; display: grid; place-items: center; width: 44px; height: 44px; border-radius: 50%; background: var(--bg); border: 2px solid var(--line-2); font-family: var(--font-mono); font-weight: 700; color: var(--fg-2); }
.rm-module.is-started .rm-module__num { border-color: var(--accent); color: var(--accent); }
.rm-module.is-done .rm-module__num { background: var(--accent-fill); border-color: var(--accent-fill); color: var(--on-fill); }
.rm-module__body { padding: 8px 0 40px; min-width: 0; }
.rm-module__head { display: flex; align-items: baseline; justify-content: space-between; flex-wrap: wrap; gap: 4px 16px; }
.rm-module__title { font-size: 1.35rem; letter-spacing: -0.02em; }
.rm-module__count { font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); }
.rm-module__summary { color: var(--fg-2); margin: 6px 0 14px; }
.rm-lessons { list-style: none; margin: 0; padding: 0; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); overflow: hidden; }
.rm-lesson + .rm-lesson { border-top: 1px solid var(--line); }
.rm-lesson__link { display: flex; align-items: center; gap: 12px; padding: 12px 16px; text-decoration: none; min-height: 48px; }
a.rm-lesson__link:hover { background: var(--surface-2); }
a.rm-lesson__link:hover .rm-lesson__title { color: var(--accent); }
.rm-lesson__title { flex: 1; font-weight: 550; min-width: 0; }
.rm-lesson.is-soon .rm-lesson__title { color: var(--fg-3); font-weight: 450; }
.rm-lesson .soon { border: 0; padding: 0; font-size: 0.7rem; opacity: 0.85; }
.rm-lesson__min { font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); white-space: nowrap; }

/* lesson status circle (roadmap + sidebar) */
.lstatus { flex: none; width: 18px; height: 18px; border-radius: 50%; border: 1.5px solid var(--line-2); display: inline-grid; place-items: center; }
.lstatus.is-done { background: var(--accent-fill); border-color: var(--accent-fill); }
.lstatus.is-done::after { content: ""; width: 8px; height: 4px; border: 2px solid var(--on-fill); border-top: 0; border-right: 0; transform: rotate(-45deg) translate(1px, -1px); }
.is-soon .lstatus { border-style: dashed; }

/* ---------- lesson page ---------- */
.lesson-layout { max-width: 1320px; margin: 0 auto; padding: 0 16px; display: grid; grid-template-columns: minmax(0, 1fr); gap: 32px; }
@media (min-width: 900px) { .lesson-layout { grid-template-columns: 240px minmax(0, 1fr); padding: 0 28px; gap: 48px; } }
@media (min-width: 1240px) { .lesson-layout { grid-template-columns: 240px minmax(0, var(--read)) 220px; justify-content: center; } }
.lesson-layout__side { order: 2; }
@media (min-width: 900px) { .lesson-layout__side { order: 0; } .lesson-layout__side .lnav { position: sticky; top: calc(var(--header-h) + 24px); max-height: calc(100vh - var(--header-h) - 48px); overflow: auto; padding-top: 40px; } }
.lesson-layout__toc { display: none; }
@media (min-width: 1240px) { .lesson-layout__toc { display: block; } .toc { position: sticky; top: calc(var(--header-h) + 24px); padding-top: 48px; } }
.lnav { font-size: 0.93rem; }
.lnav__track { display: flex; align-items: center; gap: 8px; min-height: var(--tap); text-decoration: none; color: var(--fg-2); font-weight: 600; margin-bottom: 4px; }
.lnav__track:hover { color: var(--accent); }
.lnav__details summary { cursor: pointer; font-weight: 650; padding: 6px 0; min-height: var(--tap); list-style: none; display: flex; gap: 8px; align-items: baseline; }
.lnav__details summary::-webkit-details-marker { display: none; }
.lnav__mod { font-family: var(--font-mono); font-size: 0.72rem; color: var(--accent); text-transform: uppercase; letter-spacing: 0.06em; white-space: nowrap; }
.lnav__list { list-style: none; margin: 8px 0 0; padding: 0; border-left: 1px solid var(--line); }
.lnav__item { display: flex; align-items: center; gap: 10px; min-height: var(--tap); padding: 4px 10px 4px 14px; margin-left: -1px; border-left: 2px solid transparent; text-decoration: none; color: var(--fg-2); }
.lnav__item .lstatus { width: 15px; height: 15px; }
.lnav__item .lstatus.is-done::after { width: 6px; height: 3px; }
a.lnav__item:hover { color: var(--fg); }
.lnav__item.is-current { border-left-color: var(--accent); color: var(--fg); font-weight: 600; }
.lnav__item.is-soon { color: var(--fg-3); }
.lnav__item.is-soon .soon { margin-left: auto; }
@media (max-width: 899px) { .lnav { border: 1px solid var(--line); border-radius: var(--radius); padding: 12px 16px; background: var(--surface); } }

.lesson { min-width: 0; padding: 40px 0 0; }
.crumbs { display: flex; flex-wrap: wrap; gap: 8px; font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); }
.crumbs a { color: var(--accent); text-decoration: none; }
.crumbs a:hover { text-decoration: underline; }
.lesson__title { font-size: clamp(2.1rem, 5vw, 3rem); letter-spacing: -0.035em; font-weight: 800; margin: 14px 0 14px; line-height: 1.05; }
.lesson__lead { font-family: var(--font-read); font-size: 1.22rem; line-height: 1.55; color: var(--fg-2); }
.lesson__meta { display: flex; flex-wrap: wrap; gap: 8px 20px; margin-top: 18px; padding-bottom: 24px; border-bottom: 1px solid var(--line); font-family: var(--font-mono); font-size: 0.8rem; color: var(--fg-3); align-items: center; }
.lesson__meta span { display: inline-flex; align-items: center; gap: 6px; }
.lesson__done { color: var(--good) !important; }
.toc-inline { margin: 20px 0 0; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); padding: 10px 16px; }
.toc-inline summary { cursor: pointer; font-weight: 600; min-height: var(--tap); display: flex; align-items: center; gap: 8px; }
.toc-inline ol { margin: 8px 0 4px; padding-left: 1.3em; }
.toc-inline a { color: var(--fg-2); display: inline-block; padding: 9px 0; }
.toc-inline li { line-height: 1.35; }
@media (min-width: 1240px) { .toc-inline { display: none; } }
.toc__title { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--fg-3); font-weight: 500; margin-bottom: 10px; }
.toc ol { list-style: none; margin: 0; padding: 0; border-left: 1px solid var(--line); font-size: 0.9rem; }
.toc a { display: block; padding: 5px 0 5px 14px; margin-left: -1px; border-left: 2px solid transparent; color: var(--fg-3); text-decoration: none; }
.toc a:hover { color: var(--fg); }
.toc a.is-active { color: var(--fg); border-left-color: var(--accent); }

/* reading typography */
.prose { font-family: var(--font-read); font-size: 1.14rem; line-height: 1.72; color: var(--fg); padding-top: 8px; }
@media (min-width: 720px) { .prose { font-size: 1.18rem; } }
.prose > * + * { margin-top: 1.05em; }
.prose h2 { font-family: var(--font-ui); font-size: 1.65rem; letter-spacing: -0.025em; margin-top: 2.2em; position: relative; font-weight: 750; }
.prose h3 { font-family: var(--font-ui); font-size: 1.25rem; margin-top: 1.8em; font-weight: 700; }
.prose h2 + *, .prose h3 + * { margin-top: 0.6em; }
.prose .anchor { position: absolute; left: -1.1em; padding-right: 0.3em; color: var(--fg-3); text-decoration: none; opacity: 0; font-weight: 400; }
.prose h2:hover .anchor, .prose h3:hover .anchor, .prose .anchor:focus-visible { opacity: 1; }
@media (hover: none) { .prose .anchor { display: none; } }
.prose h3 { position: relative; }
.prose a { color: var(--accent); text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 3px; }
.prose a:hover { text-decoration-thickness: 2px; }
.prose strong { font-weight: 650; }
.prose ul, .prose ol { padding-left: 1.35em; }
.prose li + li { margin-top: 0.35em; }
.prose li::marker { color: var(--fg-3); }
.prose :not(pre) > code, .prose-ui :not(pre) > code, .ws :not(pre) > code { font-size: 0.84em; padding: 0.12em 0.36em; border-radius: 5px; background: var(--surface-2); border: 1px solid var(--line); overflow-wrap: anywhere; }
.prose blockquote { margin-left: 0; padding-left: 1em; border-left: 3px solid var(--line-2); color: var(--fg-2); font-style: italic; }
.prose hr { border: 0; border-top: 1px solid var(--line); margin: 2.5em 0; }
.prose img { border-radius: var(--radius-sm); }
.link-soon { border-bottom: 1px dashed var(--line-2); cursor: help; }
.table-wrap { overflow-x: auto; -webkit-overflow-scrolling: touch; }
.prose table { border-collapse: collapse; width: 100%; font-family: var(--font-ui); font-size: 0.95rem; }
.prose th, .prose td { text-align: left; padding: 9px 12px; border-bottom: 1px solid var(--line); vertical-align: top; }
.prose thead th { font-weight: 650; border-bottom: 2px solid var(--line-2); }

.prose-ui { font-size: 1.02rem; line-height: 1.62; color: var(--fg); }
.prose-ui > * + * { margin-top: 0.75em; }
.prose-ui ul, .prose-ui ol { padding-left: 1.3em; }
.prose-ui a { color: var(--accent); }

.lesson__end { margin-top: 56px; display: grid; gap: 24px; }
.complete { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 16px; padding: 22px 20px; border-radius: 12px; border: 1px solid var(--line); background: var(--surface); }
.complete__note { font-size: 0.88rem; }
.complete__btn.is-done { background: var(--good-soft); color: var(--good); border-color: var(--good); }
.endcard { border: 1px solid var(--line); border-radius: 12px; padding: 18px 20px; background: var(--surface); }
.endcard__title { display: flex; align-items: center; gap: 8px; font-size: 1.05rem; margin-bottom: 12px; }
.endcard__title .icon { color: var(--accent); }
.archive-mini { margin: 0; padding-left: 1.2em; }
.archive-mini li + li { margin-top: 4px; }
.archive-mini a { color: var(--accent); }
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.pager__link { display: flex; flex-direction: column; gap: 4px; padding: 14px 16px; border: 1px solid var(--line); border-radius: var(--radius); text-decoration: none; background: var(--surface); min-width: 0; }
.pager__link:hover { border-color: var(--accent); }
.pager__link--next { text-align: right; align-items: flex-end; }
.pager__dir { display: inline-flex; align-items: center; gap: 4px; font-family: var(--font-mono); font-size: 0.75rem; color: var(--fg-3); text-transform: uppercase; letter-spacing: 0.06em; }
.pager__title { font-weight: 650; color: var(--accent); overflow-wrap: anywhere; }

/* ==========================================================================
   components
   ========================================================================== */
.prose .code, .prose .tracer, .prose .quiz, .prose .callout, .prose .tryit, .prose .convo, .prose .fig, .prose .cx { font-family: var(--font-ui); font-size: 1rem; line-height: 1.55; margin-top: 1.6em; margin-bottom: 1.6em; }
.prose .code + *, .prose .tracer + *, .prose .quiz + *, .prose .callout + *, .prose .tryit + *, .prose .convo + *, .prose .fig + *, .prose .cx + * { margin-top: 0; }
.prose :is(.code, .tracer, .quiz, .callout, .tryit, .convo, .fig, .cx) + h2 { margin-top: 1.5em; }
.prose :is(.code, .tracer, .quiz, .callout, .tryit, .convo, .fig, .cx) + h3 { margin-top: 1.1em; }
.prose :is(.callout, .convo) + :is(.callout, .convo) { margin-top: -0.6em; }

/* code blocks */
.code { border: 1px solid var(--line); border-radius: var(--radius); background: var(--code-bg); overflow: hidden; }
.code__bar { display: flex; align-items: center; gap: 8px; padding: 0 4px 0 12px; min-height: var(--tap); border-bottom: 1px solid var(--code-line); background: color-mix(in srgb, var(--code-bg) 70%, var(--surface-2)); }
.code__title, .code__lang { font-family: var(--font-mono); font-size: 0.76rem; color: var(--fg-3); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.code__title { margin-right: 4px; }
.code__tabs { display: flex; gap: 2px; align-self: stretch; }
.code__tab { position: relative; border: 0; background: none; padding: 0 10px; min-height: var(--tap); font-family: var(--font-mono); font-size: 0.8rem; color: var(--fg-3); }
.code__tab:hover { color: var(--fg); }
.code__tab[aria-selected="true"] { color: var(--fg); }
.code__tab[aria-selected="true"]::after { content: ""; position: absolute; left: 8px; right: 8px; bottom: -1px; height: 2px; background: var(--accent); }
.code__copy { margin-left: auto; display: inline-flex; align-items: center; gap: 6px; border: 0; background: none; color: var(--fg-3); font-size: 0.8rem; padding: 0 10px; min-height: var(--tap); border-radius: 6px; }
.code__copy:hover { color: var(--fg); background: var(--surface-2); }
.code__copy .icon { width: 15px; height: 15px; }
.code__pre { margin: 0; padding: 14px 0; overflow-x: auto; font-size: 0.86rem; line-height: 1.65; tab-size: 4; }
.code__pre code { display: block; min-width: max-content; counter-reset: ln; }
.code__pre code { white-space: pre; padding-right: 16px; }
.code__pre .ln { white-space: pre; }
.code__pre .ln::before { counter-increment: ln; content: counter(ln); display: inline-block; width: 2.6em; padding-right: 1em; text-align: right; color: var(--fg-3); opacity: 0.6; user-select: none; }
.code--single .code__pre .ln::before { content: none; }
.code--single .code__pre code { padding-left: 16px; }
/* JS/Python switching: one choice for the whole site */
.code__pane[data-lang="py"] { display: none; }
:root[data-lang="py"] .code__pane[data-lang="js"] { display: none; }
:root[data-lang="py"] .code__pane[data-lang="py"] { display: block; }
.code--single .code__pane { display: block !important; }
.tk-k { color: var(--tk-k); }
.tk-s { color: var(--tk-s); }
.tk-n { color: var(--tk-n); }
.tk-c { color: var(--tk-c); font-style: italic; }
.tk-f { color: var(--tk-f); }
.tk-l { color: var(--tk-l); }
.tk-b { color: var(--tk-b); }
.tk-t { color: var(--tk-t); }
.tk-o { color: var(--tk-o); }
.tk-p { color: var(--tk-p); }

/* callouts */
.callout { --c: var(--accent); --c-soft: var(--accent-soft); border: 1px solid color-mix(in srgb, var(--c) 30%, var(--line)); border-left: 4px solid var(--c); background: var(--c-soft); border-radius: var(--radius); padding: 14px 18px 16px; }
.callout--mistake { --c: var(--bad); --c-soft: var(--bad-soft); }
.callout--tip { --c: var(--good); --c-soft: var(--good-soft); }
.callout--real-world { --c: var(--info); --c-soft: var(--info-soft); }
.callout__head { display: flex; align-items: center; gap: 8px; font-family: var(--font-mono); font-size: 0.76rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--c); font-weight: 700; margin-bottom: 6px; }
.callout__body > * + * { margin-top: 0.6em; }
.callout__body a { color: inherit; }

/* tracer */
.tracer { border: 1px solid var(--line); border-radius: 12px; background: var(--surface); overflow: hidden; }
.tracer__head { display: flex; align-items: center; gap: 8px; padding: 10px 14px; border-bottom: 1px solid var(--line); font-weight: 650; font-size: 0.95rem; }
.tracer__head .icon { color: var(--accent); }
.tracer__title { min-width: 0; }
.tracer__hint { margin-left: auto; font-family: var(--font-mono); font-size: 0.72rem; color: var(--fg-3); font-weight: 400; white-space: nowrap; }
@media (max-width: 600px) { .tracer__hint { display: none; } }
.tracer__body { display: grid; }
.tracer--code .tracer__body { grid-template-columns: minmax(0, 1fr); }

.tracer__code { background: var(--code-bg); border-bottom: 1px solid var(--line); overflow-x: auto; }

.tracer__code { max-height: 220px; overflow-y: auto; }
.tracer__code pre { margin: 0; padding: 10px 0; font-size: 0.8rem; line-height: 1.7; }
.tracer__code code { display: block; min-width: max-content; }
.tracer__code .ln { display: block; padding: 0 14px; white-space: pre; border-left: 3px solid transparent; }
.tracer__code .ln.is-active { background: var(--accent-soft); border-left-color: var(--accent); }
.tracer__steps { list-style: none; margin: 0; padding: 0; min-width: 0; }
.tracer__step { padding: 18px 16px 14px; display: flex; flex-direction: column; gap: 14px; min-width: 0; }
html:not(.js) .tracer__step + .tracer__step { border-top: 1px dashed var(--line); }
.js .tracer .tracer__step:not(:first-child), .js .tracer[data-ready] .tracer__step { display: none; }
.js .tracer[data-ready] .tracer__step.is-current { display: flex; }
.tracer__state { display: flex; flex-direction: column; gap: 14px; align-items: center; min-width: 0; overflow-x: auto; padding-bottom: 4px; }
.tracer__caption { font-size: 0.98rem; color: var(--fg); display: flex; gap: 10px; align-items: baseline; min-height: 3em; }
.tracer__num { flex: none; font-family: var(--font-mono); font-size: 0.72rem; color: var(--on-fill); background: var(--accent-fill); border-radius: 4px; padding: 0.1em 0.45em; }
.tracer__controls { display: flex; align-items: center; gap: 8px; padding: 10px 12px; border-top: 1px solid var(--line); background: var(--surface-2); }
html:not(.js) .tracer__controls { display: none; }
.tracer__range { flex: 1; min-width: 40px; height: var(--tap); margin: 0 4px; accent-color: var(--accent-fill); cursor: pointer; }
.tracer__count { font-family: var(--font-mono); font-size: 0.8rem; color: var(--fg-2); white-space: nowrap; min-width: 4.5em; text-align: right; }
.tracer__play .i-pause { display: none; }
.tracer.is-playing .tracer__play .i-pause { display: block; }
.tracer.is-playing .tracer__play .i-play { display: none; }
.tr-label { font-family: var(--font-mono); font-size: 0.74rem; color: var(--fg-3); margin-bottom: 6px; text-align: center; }
.tr-array { max-width: 100%; }
.tr-cells { display: flex; align-items: flex-start; gap: 4px; }
.tr-cell { display: flex; flex-direction: column; align-items: center; gap: 3px; min-width: 0; }
.tr-idx { font-family: var(--font-mono); font-size: 0.66rem; color: var(--fg-3); line-height: 1; }
.tr-val { display: grid; place-items: center; min-width: 42px; height: 42px; padding: 0 6px; border-radius: 7px; border: 1.5px solid var(--line-2); background: var(--bg); font-family: var(--font-mono); font-weight: 600; font-size: 0.95rem; transition: background 0.2s, border-color 0.2s, opacity 0.2s, transform 0.2s; }
@media (max-width: 480px) { .tr-val { min-width: 34px; height: 36px; font-size: 0.85rem; padding: 0 4px; } }
.tr-val--long { font-size: 0.8rem; }
.tr-ptr { font-family: var(--font-mono); font-size: 0.72rem; font-weight: 700; color: var(--accent); min-height: 1.2em; line-height: 1.2; white-space: nowrap; }
.tr-cell.is-hl .tr-val { border-color: var(--accent); background: var(--accent-soft); box-shadow: 0 0 0 2px var(--accent-soft); }
.tr-cell.is-mark .tr-val { border-color: var(--good); background: var(--good-soft); color: var(--good); }
.tr-cell.is-dim { opacity: 0.38; }
.tr-cell.is-changed .tr-val { animation: tr-pop 0.5s ease; }
.tr-cell--ghost .tr-val { border-style: dashed; background: transparent; opacity: 0.5; }
.tr-arrow { align-self: center; margin-top: -6px; color: var(--fg-3); font-family: var(--font-mono); }
.tr-null { align-self: center; margin-top: -6px; font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); }
.tr-array--list .tr-cells { gap: 6px; }
@keyframes tr-pop { 0% { transform: scale(1); } 40% { transform: scale(1.12); } 100% { transform: scale(1); } }
@media (prefers-reduced-motion: reduce) { .tr-cell.is-changed .tr-val { animation: none; } }
.tr-vars { display: flex; flex-wrap: wrap; justify-content: center; gap: 6px 8px; margin: 0; }
.tr-var { display: flex; align-items: center; border: 1px solid var(--line); border-radius: 6px; overflow: hidden; font-family: var(--font-mono); font-size: 0.82rem; }
.tr-var dt { padding: 3px 8px; background: var(--surface-2); color: var(--fg-3); }
.tr-var dd { margin: 0; padding: 3px 9px; font-weight: 600; }
.tr-var.is-changed { border-color: var(--accent); }
.tr-var.is-changed dd { background: var(--accent-soft); }
.tr-gridwrap { max-width: 100%; overflow-x: auto; }
.tr-grid { border-collapse: separate; border-spacing: 3px; font-family: var(--font-mono); font-size: 0.86rem; }
.tr-grid td { min-width: 36px; height: 34px; text-align: center; border: 1.5px solid var(--line-2); border-radius: 6px; background: var(--bg); font-weight: 600; padding: 0 5px; }
.tr-grid th { font-weight: 500; color: var(--fg-3); font-size: 0.74rem; padding: 0 4px; }
.tr-grid td.is-hl { border-color: var(--accent); background: var(--accent-soft); }
.tr-grid td.is-mark { border-color: var(--good); background: var(--good-soft); color: var(--good); }
.tr-grid td.is-dim { opacity: 0.38; }
.tr-tree, .tr-graph { width: 100%; max-width: 420px; }
.tr-tree svg, .tr-graph svg { width: 100%; height: auto; display: block; overflow: visible; }
.tr-edge { stroke: var(--line-2); stroke-width: 2; }
.tr-edge.is-hl { stroke: var(--accent); stroke-width: 3; }
.tr-node circle { fill: var(--bg); stroke: var(--line-2); stroke-width: 2; }
.tr-node text { fill: var(--fg); font-family: var(--font-mono); font-size: 13px; font-weight: 600; }
.tr-node.is-hl circle { stroke: var(--accent); fill: var(--accent-soft); stroke-width: 3; }
.tr-node.is-mark circle { stroke: var(--good); fill: var(--good-soft); stroke-width: 3; }
.tr-node.is-dim { opacity: 0.35; }
.tr-weight, .tr-nodelabel { fill: var(--fg-3); font-family: var(--font-mono); font-size: 11px; }
.tr-nodelabel { fill: var(--accent); font-weight: 600; }
.tr-arrowhead { fill: var(--line-2); }

/* quiz */
.quiz { border: 1px solid var(--line); border-radius: 12px; background: var(--surface); padding: 6px 18px 18px; }
.quiz__head { display: flex; align-items: center; gap: 8px; font-family: var(--font-mono); font-size: 0.76rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--accent); font-weight: 700; padding: 12px 0 4px; }
.quiz__q + .quiz__q { margin-top: 18px; padding-top: 16px; border-top: 1px solid var(--line); }
.quiz__prompt { font-weight: 600; font-size: 1.05rem; margin: 6px 0 12px; }
.quiz__options { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.quiz__opt { width: 100%; display: flex; align-items: flex-start; gap: 12px; text-align: left; padding: 11px 14px; border-radius: 9px; border: 1.5px solid var(--line); background: var(--bg); color: var(--fg); line-height: 1.45; transition: border-color 0.15s, background 0.15s; }
.quiz__opt:hover:not([disabled]) { border-color: var(--line-2); background: var(--surface-2); }
.quiz__letter { flex: none; display: grid; place-items: center; width: 24px; height: 24px; border-radius: 6px; border: 1px solid var(--line-2); font-family: var(--font-mono); font-size: 0.78rem; font-weight: 700; color: var(--fg-2); }
.quiz__text { flex: 1; min-width: 0; }
.quiz__icon { display: none; margin-top: 2px; }
.quiz__opt.is-right { border-color: var(--good); background: var(--good-soft); }
.quiz__opt.is-right .quiz__icon--ok { display: block; color: var(--good); }
.quiz__opt.is-right .quiz__letter { border-color: var(--good); color: var(--good); }
.quiz__opt.is-wrong { border-color: var(--bad); background: var(--bad-soft); }
.quiz__opt.is-wrong .quiz__icon--no { display: block; color: var(--bad); }
.quiz__opt.is-wrong .quiz__letter { border-color: var(--bad); color: var(--bad); }
.quiz__opt[disabled] { cursor: default; }
.quiz__opt[disabled]:not(.is-right):not(.is-wrong) { opacity: 0.6; }
.quiz__why { margin: 6px 2px 4px 38px; font-size: 0.95rem; color: var(--fg-2); }

/* complexity */
.cx--badges { display: flex; flex-wrap: wrap; gap: 10px 14px; align-items: flex-start; }
.cx__item { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; padding: 10px 14px; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); }
.cx__k { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); }
.cx__why { flex-basis: 100%; font-size: 0.92rem; color: var(--fg-2); }
.cx__note { flex-basis: 100%; color: var(--fg-2); font-size: 0.95rem; }
.bigo { font-family: var(--font-mono); font-weight: 700; font-size: 0.92rem; color: var(--accent); background: var(--accent-soft); border-radius: 6px; padding: 0.15em 0.5em; white-space: nowrap; }
.cx__table { width: 100%; border-collapse: collapse; font-size: 0.95rem; border: 1px solid var(--line); border-radius: var(--radius); }
.cx__table th, .cx__table td { padding: 10px 12px; text-align: left; border-bottom: 1px solid var(--line); vertical-align: top; }
.cx__table thead th { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); font-weight: 500; background: var(--surface-2); }
.cx__table tbody th { font-weight: 600; }
.cx__table tbody tr:last-child > * { border-bottom: 0; }

/* figures (inline SVG, themed) */
.fig, .tracer, .convo { margin-left: 0; margin-right: 0; }
.fig__media { border: 1px solid var(--line); border-radius: 12px; background: var(--surface); padding: 18px; display: flex; justify-content: center; overflow-x: auto; }
.fig__media svg { width: 100%; max-width: 640px; height: auto; max-height: 460px; overflow: visible; }
.fig figcaption { font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); text-align: center; margin-top: 10px; }
.fig svg text { fill: var(--fg); font-family: var(--font-mono); font-size: 14px; }
.fig svg .t-sans { font-family: var(--font-ui); }
.fig svg .t-small { font-size: 11px; }
.fig svg .t-big { font-size: 18px; font-weight: 700; }
.fig svg .t-bold { font-weight: 700; }
.fig svg .f-fg { fill: var(--fg); }
.fig svg .f-muted { fill: var(--fg-3); }
.fig svg .f-bg { fill: var(--bg); }
.fig svg .f-surface { fill: var(--surface-2); }
.fig svg .f-accent { fill: var(--accent); }
.fig svg .f-accent-soft { fill: var(--accent-soft); }
.fig svg .f-good { fill: var(--good); }
.fig svg .f-good-soft { fill: var(--good-soft); }
.fig svg .f-bad { fill: var(--bad); }
.fig svg .f-bad-soft { fill: var(--bad-soft); }
.fig svg .f-info { fill: var(--info); }
.fig svg .f-none { fill: none; }
.fig svg .s-fg { stroke: var(--fg); }
.fig svg .s-muted { stroke: var(--fg-3); }
.fig svg .s-line { stroke: var(--line-2); }
.fig svg .s-accent { stroke: var(--accent); }
.fig svg .s-good { stroke: var(--good); }
.fig svg .s-bad { stroke: var(--bad); }
.fig svg .s-info { stroke: var(--info); }
.fig svg .s-thin { stroke-width: 1; }
.fig svg .s-thick { stroke-width: 3; }
.fig svg .s-dash { stroke-dasharray: 5 4; }

/* try it */
.tryit { border: 1.5px dashed color-mix(in srgb, var(--accent) 55%, var(--line)); border-radius: 12px; padding: 16px 18px 18px; background: var(--surface); }
.tryit__head { display: flex; align-items: center; gap: 8px; font-family: var(--font-mono); font-size: 0.76rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--accent); font-weight: 700; margin-bottom: 8px; }
.tryit__task > * + * { margin-top: 0.6em; }
.tryit__label { display: block; margin: 14px 0 6px; font-weight: 600; font-size: 0.9rem; }
.tryit__input { width: 100%; border: 1px solid var(--line-2); border-radius: 8px; background: var(--bg); padding: 10px 12px; font-family: var(--font-mono); font-size: 0.86rem; line-height: 1.55; resize: vertical; min-height: 6em; }
.tryit__input:focus { outline: 2px solid var(--accent); outline-offset: 0; border-color: transparent; }
.tryit__answer { margin-top: 12px; }
.tryit__answer summary { display: inline-flex; align-items: center; gap: 8px; cursor: pointer; font-weight: 600; color: var(--accent); padding: 0; min-height: var(--tap); list-style: none; }
.tryit__answer summary::-webkit-details-marker { display: none; }
.tryit__answer-body { margin-top: 8px; padding: 14px 16px; border-radius: 9px; background: var(--accent-soft); }
.tryit__answer-body > * + * { margin-top: 0.7em; }
.tryit__answer-body .convo, .tryit__answer-body .code { margin: 0.8em 0; }

/* prompt / response */
.convo { border: 1px solid var(--line); border-radius: 12px; overflow: hidden; background: var(--surface); }
.convo__head { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 6px 12px; padding: 10px 14px; border-bottom: 1px solid var(--line); background: var(--surface-2); }
.convo__label { display: inline-flex; align-items: center; gap: 7px; font-weight: 700; font-size: 0.9rem; }
.convo__label--weak { color: var(--bad); }
.convo__label--good { color: var(--good); }
.convo__note { font-family: var(--font-mono); font-size: 0.7rem; color: var(--fg-3); }
.convo__turn { padding: 12px 16px 14px; }
.convo__turn + .convo__turn { border-top: 1px solid var(--line); }
.convo__role { font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--fg-3); font-weight: 700; margin-bottom: 5px; }
.convo__text { white-space: pre-wrap; overflow-wrap: anywhere; }
.convo__turn--user .convo__text, .convo__turn--system .convo__text { font-family: var(--font-mono); font-size: 0.86rem; line-height: 1.6; }
.convo__turn--system { background: var(--bg-2); }
.convo__turn--model { border-left: 3px solid var(--accent); }
.convo__turn--model .convo__role { color: var(--accent); }
.convo--weak .convo__turn--model { border-left-color: var(--bad); }
.convo--weak .convo__turn--model .convo__role { color: var(--bad); }
.convo--good .convo__turn--model { border-left-color: var(--good); }
.convo--good .convo__turn--model .convo__role { color: var(--good); }

/* ==========================================================================
   practice list
   ========================================================================== */
.pstats { margin-top: 28px; display: flex; flex-wrap: wrap; gap: 20px 40px; align-items: center; padding: 18px 20px; border: 1px solid var(--line); border-radius: 12px; background: var(--surface); max-width: 44rem; }
.pstats__main { display: flex; align-items: baseline; gap: 8px; }
.pstats__num { font-size: 2.6rem; font-weight: 800; letter-spacing: -0.04em; color: var(--accent); line-height: 1; }
.pstats__of { color: var(--fg-2); }
.pstats__bars { flex: 1; min-width: 220px; display: grid; gap: 8px; }
.pstats__row { display: grid; grid-template-columns: 70px 1fr 56px; align-items: center; gap: 10px; font-size: 0.85rem; }
.pstats__row .muted { text-align: right; font-family: var(--font-mono); font-size: 0.78rem; }
.diff { display: inline-flex; align-items: center; justify-content: center; font-family: var(--font-mono); font-size: 0.72rem; font-weight: 700; padding: 0.18em 0.6em; border-radius: 99px; white-space: nowrap; }
.diff--easy { color: var(--good); background: var(--good-soft); }
.diff--medium { color: var(--warn); background: color-mix(in srgb, var(--warn) 13%, transparent); }
.diff--hard { color: var(--bad); background: var(--bad-soft); }
.filters { position: sticky; top: var(--header-h); z-index: 10; display: flex; flex-wrap: wrap; gap: 10px; align-items: center; padding: 14px 0; margin-top: 8px; background: var(--bg); border-bottom: 1px solid var(--line); }
.filters label { display: flex; }
.filters__search { flex: 1 1 240px; position: relative; align-items: center; }
.filters__search .icon { position: absolute; left: 12px; color: var(--fg-3); pointer-events: none; }
.filters input[type="search"], .filters select { height: var(--tap); border-radius: 8px; border: 1px solid var(--line-2); background: var(--surface); padding: 0 12px; min-width: 0; }
.filters input[type="search"] { width: 100%; padding-left: 38px; }
.filters select { max-width: 100%; }
@media (min-width: 601px) { .filters select { width: 11.5rem; } .filters [data-f="status"] { width: 9rem; } }
@media (max-width: 600px) { .filters label:not(.filters__search) { flex: 1 1 40%; } .filters select { width: 100%; } .filters { position: static; } }
.filters__result { min-height: 1.5em; margin: 10px 0 0; font-size: 0.9rem; }
.seg { display: inline-flex; border: 1px solid var(--line-2); border-radius: 9px; padding: 2px; background: var(--surface); gap: 2px; }
.seg__btn { border: 0; background: none; padding: 0 12px; border-radius: 7px; font-size: 0.9rem; font-weight: 550; color: var(--fg-2); min-height: max(34px, calc(var(--tap) - 6px)); }
.seg__btn:hover { color: var(--fg); }
.seg__btn[aria-pressed="true"] { background: var(--accent-fill); color: var(--on-fill); }
.seg--sm .seg__btn { padding: 0 10px; font-size: 0.85rem; min-height: max(32px, calc(var(--tap) - 6px)); }
.ptopic { padding-top: 36px; }
.ptopic__head { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.ptopic__title { font-size: 1.4rem; letter-spacing: -0.02em; }
.ptopic__count { font-family: var(--font-mono); font-size: 0.8rem; }
.ptopic__summary { margin: 4px 0 14px; }
.ptopic__summary a { color: var(--accent); }
.ptopic__empty { padding: 16px; border: 1px dashed var(--line-2); border-radius: var(--radius); color: var(--fg-3); }
.plist { list-style: none; margin: 0; padding: 0; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); overflow: hidden; }
.plist__row { position: relative; display: grid; grid-template-columns: 20px minmax(0, 1fr) auto auto; grid-template-areas: "dot title pattern diff" "dot aka pattern diff"; align-items: center; column-gap: 14px; padding: 12px 16px; min-height: 52px; }
.plist__row + .plist__row { border-top: 1px solid var(--line); }
.plist__row:hover { background: var(--surface-2); }
.plist__row .pstatus { grid-area: dot; }
.plist__title { grid-area: title; font-weight: 600; text-decoration: none; min-width: 0; }
.plist__title::after { content: ""; position: absolute; inset: 0; }
.plist__row:hover .plist__title { color: var(--accent); }
.plist__aka { grid-area: aka; font-size: 0.82rem; color: var(--fg-3); }
.plist__aka:empty { display: none; }
.plist__pattern { grid-area: pattern; font-family: var(--font-mono); font-size: 0.75rem; color: var(--fg-3); white-space: nowrap; }
.plist__row .diff { grid-area: diff; min-width: 64px; }
@media (max-width: 560px) {
  .plist__row { grid-template-columns: 20px minmax(0, 1fr) auto; grid-template-areas: "dot title diff" "dot aka diff" "dot pattern diff"; }
  .plist__pattern { white-space: normal; }
}
.plist--compact .plist__row { grid-template-areas: "dot title pattern diff"; }
@media (min-width: 720px) {
  .plist__row { grid-template-columns: 20px auto minmax(0, 1fr) auto auto; grid-template-areas: "dot title aka pattern diff"; min-height: 50px; padding: 8px 16px; }
  .plist__aka { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
  .plist__aka:not(:empty)::before { content: ""; display: inline-block; width: 1px; height: 0.9em; margin-right: 10px; vertical-align: -0.1em; background: var(--line-2); }
  .plist--compact .plist__row { grid-template-areas: "dot title aka pattern diff"; }
}
.pstatus { width: 16px; height: 16px; border-radius: 50%; border: 1.5px solid var(--line-2); display: inline-block; flex: none; }
.pstatus.is-attempted { border-color: var(--warn); background: conic-gradient(var(--warn) 0 50%, transparent 50% 100%); }
.pstatus.is-solved { border-color: var(--good); background: var(--good); box-shadow: inset 0 0 0 3px var(--surface); }

/* ==========================================================================
   workspace
   ========================================================================== */
.is-workspace main { display: flex; }
.ws { flex: 1; display: grid; grid-template-columns: minmax(0, 1fr); min-width: 0; width: 100%; }
@media (min-width: 1000px) {
  .ws { grid-template-columns: minmax(0, 1fr) minmax(0, 1.05fr); height: calc(100vh - var(--header-h)); height: calc(100dvh - var(--header-h)); }
  .ws__problem { overflow-y: auto; border-right: 1px solid var(--line); }
  .ws__code { height: 100%; min-height: 0; }
}
.ws__scroll { padding: 24px 16px 48px; max-width: 760px; margin: 0 auto; }
@media (min-width: 720px) { .ws__scroll { padding: 32px 32px 64px; } }
.ws__title { display: flex; align-items: center; gap: 12px; font-size: clamp(1.7rem, 3.4vw, 2.3rem); letter-spacing: -0.03em; font-weight: 800; margin: 12px 0 10px; }
.ws__title .pstatus { width: 18px; height: 18px; }
.ws__badges { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 10px; margin-bottom: 22px; }
.aka { font-size: 0.88rem; color: var(--fg-3); }
.aka strong { color: var(--fg-2); font-weight: 600; }
.ws__story { font-size: 1.06rem; }
.ws__h { display: flex; align-items: center; gap: 8px; font-size: 1.1rem; margin: 30px 0 10px; letter-spacing: -0.01em; }
.ws__h .icon { color: var(--accent); }
.sig { margin-top: 12px; font-size: 0.92rem; }
.sig code { display: inline-block; max-width: 100%; overflow-wrap: anywhere; }
.example { border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); margin-top: 12px; overflow: hidden; }
.example__head { font-family: var(--font-mono); font-size: 0.74rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); padding: 8px 14px; border-bottom: 1px solid var(--line); background: var(--surface-2); }
.example__io { display: grid; gap: 10px; padding: 12px 14px 0; }
@media (min-width: 560px) { .example__io { grid-template-columns: 1.4fr 1fr; } }
.example__k { display: block; font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); margin-bottom: 4px; }
.io { margin: 0; padding: 8px 10px; border-radius: 7px; background: var(--code-bg); border: 1px solid var(--code-line); font-size: 0.84rem; line-height: 1.55; white-space: pre-wrap; overflow-wrap: anywhere; }
.example__why { padding: 12px 14px 14px; font-size: 0.97rem; }
.example__why > p + p { margin-top: 0.5em; }
.constraints { margin: 0; padding-left: 1.2em; font-family: var(--font-mono); font-size: 0.86rem; color: var(--fg-2); }
.constraints li + li { margin-top: 3px; }
.brute { margin-top: 28px; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); }
.brute summary { display: flex; align-items: center; gap: 8px; padding: 12px 14px; cursor: pointer; font-weight: 650; list-style: none; }
.brute summary::-webkit-details-marker { display: none; }
.brute summary .icon { color: var(--warn); }
.brute[open] summary { border-bottom: 1px solid var(--line); }
.brute .prose-ui { padding: 12px 16px 16px; }
.hints { margin-top: 12px; }
.hints__head { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; flex-wrap: wrap; }
.hints__head .muted { font-family: var(--font-mono); font-size: 0.78rem; }
.hints__list { list-style: none; margin: 0 0 12px; padding: 0; display: grid; gap: 8px; }
.hint { display: flex; flex-direction: column; gap: 4px; padding: 12px 14px; border-radius: var(--radius); background: var(--accent-soft); border-left: 3px solid var(--accent); animation: hint-in 0.25s ease; }
@keyframes hint-in { from { opacity: 0; transform: translateY(-4px); } }
@media (prefers-reduced-motion: reduce) { .hint { animation: none; } }
.hint__n { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--accent); font-weight: 700; }
.hint__body > * + * { margin-top: 0.5em; }
.solution { margin-top: 36px; }
.solution__lock { display: grid; grid-template-columns: auto 1fr; gap: 6px 14px; align-items: start; padding: 18px; border: 1px dashed var(--line-2); border-radius: 12px; }
.solution__lock > .icon { width: 26px; height: 26px; color: var(--fg-3); margin-top: 2px; }
.solution__lock h2 { font-size: 1.1rem; margin-bottom: 4px; }
.solution__lock p { color: var(--fg-2); font-size: 0.95rem; }
.solution__lock .btn { grid-column: 2; justify-self: start; margin-top: 8px; }
.solution__body > h2 { display: flex; align-items: center; gap: 8px; font-size: 1.3rem; margin-bottom: 12px; }
.solution__body > h2 .icon { color: var(--accent); }
.solution__body > * + * { margin-top: 18px; }
.ws__related { margin-top: 36px; display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }

.ws__code { display: flex; flex-direction: column; min-width: 0; background: var(--surface); border-top: 1px solid var(--line); }
@media (min-width: 1000px) { .ws__code { border-top: 0; } }
.ws__toolbar { display: flex; align-items: center; gap: 10px; padding: 10px 12px; border-bottom: 1px solid var(--line); }
.ws__save { margin-left: auto; font-family: var(--font-mono); font-size: 0.74rem; }
.editor { position: relative; flex: 1 1 auto; min-height: 340px; background: var(--code-bg); overflow: hidden; display: flex; }
@media (min-width: 1000px) { .editor { min-height: 200px; } }
.editor > * { flex: 1; min-width: 0; }
.editor__fallback { width: 100%; min-height: 340px; border: 0; resize: vertical; background: var(--code-bg); padding: 14px; font-family: var(--font-mono); font-size: 0.88rem; line-height: 1.6; tab-size: 4; }
.editor .cm-editor { height: 100%; font-size: 0.9rem; }
@media (max-width: 999px) { .editor .cm-editor { max-height: 70vh; } }
.editor .cm-editor.cm-focused { outline: none; }
.editor .cm-scroller { font-family: var(--font-mono); line-height: 1.6; }
.ws__actions { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 10px; padding: 10px 12px; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.ws__kbd { margin-left: auto; font-size: 0.78rem; }
@media (max-width: 600px) { .ws__kbd { display: none; } }
.custom { padding: 10px 12px 12px; border-bottom: 1px solid var(--line); display: grid; gap: 8px; }
.custom label { font-size: 0.85rem; color: var(--fg-2); }
.custom__input { width: 100%; font-family: var(--font-mono); font-size: 0.84rem; border: 1px solid var(--line-2); border-radius: 7px; background: var(--bg); padding: 8px 10px; resize: vertical; }
.custom .btn { justify-self: start; }
.results { flex: 0 1 auto; max-height: 46%; overflow-y: auto; padding: 12px 14px 18px; background: var(--surface); }
@media (max-width: 999px) { .results { max-height: none; } }
.results__empty { font-size: 0.92rem; }
.results__summary { display: flex; align-items: center; flex-wrap: wrap; gap: 8px 12px; margin-bottom: 12px; }
.results__verdict { display: inline-flex; align-items: center; gap: 6px; font-weight: 750; font-size: 1.1rem; }
.results__verdict .icon { width: 20px; height: 20px; }
.results__verdict.is-pass { color: var(--good); }
.results__verdict.is-fail { color: var(--bad); }
.results__verdict.is-busy { color: var(--fg-2); }
.results__meta { font-family: var(--font-mono); font-size: 0.78rem; color: var(--fg-3); }
.results__tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 10px; }
.rtab { display: inline-flex; align-items: center; gap: 5px; min-height: max(32px, calc(var(--tap) - 4px)); padding: 0 10px 0 7px; border-radius: 7px; border: 1px solid var(--line); background: var(--bg); color: var(--fg-2); font-family: var(--font-mono); font-size: 0.78rem; }
.rtab .icon { width: 14px; height: 14px; }
.rtab.is-pass .icon { color: var(--good); }
.rtab.is-fail { color: var(--fg); border-color: color-mix(in srgb, var(--bad) 45%, var(--line)); }
.rtab.is-fail .icon { color: var(--bad); }
.rtab.is-skip { color: var(--fg-3); border-style: dashed; }
.rtab[aria-selected="true"] { border-color: var(--fg-2); background: var(--surface-2); color: var(--fg); box-shadow: inset 0 -2px 0 var(--fg-2); }
.rcase { display: grid; gap: 10px; }
.rcase__row > span { display: block; font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.07em; color: var(--fg-3); margin-bottom: 4px; }
.rcase__tag { display: inline-flex; align-items: center; gap: 3px; margin-left: 6px; font-weight: 700; letter-spacing: 0.04em; }
.rcase__tag .icon { width: 12px; height: 12px; }
.is-pass > span > .rcase__tag { color: var(--good); }
.is-fail > span > .rcase__tag { color: var(--bad); }
.rcase__row--got.is-fail .io { border-color: var(--bad); background: var(--bad-soft); }
.rcase__row--got.is-pass .io { border-color: var(--good); }
.rcase__err .io { border-color: var(--bad); color: var(--bad); background: var(--bad-soft); }
.rcase__msg { font-size: 0.9rem; color: var(--fg-2); }
.loader { width: 14px; height: 14px; border-radius: 50%; border: 2px solid var(--line-2); border-top-color: var(--accent); animation: spin 0.8s linear infinite; display: inline-block; }
@keyframes spin { to { transform: rotate(360deg); } }
.ws__jump { display: none; }
@media (max-width: 999px) {
  .ws__jump { position: fixed; z-index: 40; right: 16px; bottom: max(16px, env(safe-area-inset-bottom)); display: inline-flex; align-items: center; gap: 6px; min-height: 48px; padding: 0 18px; border-radius: 99px; background: var(--fg); color: var(--bg); font-weight: 650; font-size: 0.95rem; text-decoration: none; box-shadow: 0 6px 20px rgba(0, 0, 0, 0.22); }
  .ws__jump-icon { transform: rotate(90deg); }
  .ws__jump.is-up .ws__jump-icon { transform: rotate(-90deg); }
  .ws__scroll { padding-bottom: 88px; }
  .results { padding-bottom: 88px; }
}
.ws__problem:focus, .ws__code:focus { outline: none; }
.solved-banner { display: flex; gap: 10px; align-items: center; padding: 10px 12px; border-radius: 9px; background: var(--good-soft); color: var(--good); font-weight: 600; margin-bottom: 12px; }
.solved-banner a { color: inherit; }

/* ==========================================================================
   archive / legacy / about / 404
   ========================================================================== */
.archive { list-style: none; margin: 0; padding: 0; display: grid; gap: 14px; }
.arch { display: grid; grid-template-columns: 1fr; gap: 14px; padding: 16px; border: 1px solid var(--line); border-radius: 12px; background: var(--surface); }
@media (min-width: 640px) { .arch { grid-template-columns: 150px 1fr; gap: 20px; } }
.arch__img img { width: 100%; aspect-ratio: 4 / 3; object-fit: cover; border-radius: 8px; display: block; }
@media (max-width: 639px) { .arch__img img { aspect-ratio: 16 / 7; } }
.arch__meta { display: flex; gap: 10px; align-items: center; font-family: var(--font-mono); font-size: 0.76rem; color: var(--fg-3); }
.arch__title { font-size: 1.25rem; margin: 6px 0; }
.arch__title a { text-decoration: none; display: inline-block; padding: 8px 0; margin: -8px 0; }
.arch__title a:hover { color: var(--accent); }
.arch__excerpt { color: var(--fg-2); }
.arch__rel { display: flex; gap: 6px; align-items: baseline; flex-wrap: wrap; margin-top: 8px; font-size: 0.9rem; }
.arch__rel a { color: var(--accent); }
.legacy { padding-top: 40px; max-width: var(--read); margin: 0 auto; }
.legacy .callout { margin-top: 24px; }
.legacy__cover { margin: 28px 0 0; }
.legacy__cover img { width: auto; max-width: 100%; height: auto; margin: 0 auto; border-radius: 12px; display: block; border: 1px solid var(--line); background: #fff; }
.legacy__cover figcaption, .legacy .fig-caption { display: block; font-family: var(--font-mono); font-size: 0.76rem; color: var(--fg-3); text-align: center; margin-top: 8px; }
.legacy__body pre { background: var(--code-bg); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 16px; overflow-x: auto; font-size: 0.86rem; line-height: 1.6; }
.legacy__body pre code { background: none; border: 0; padding: 0; font-size: inherit; }
.legacy__body .fig-center { display: flex; flex-direction: column; align-items: center; gap: 6px; }
.legacy__body .embed-center { display: flex; justify-content: center; }
.legacy__body .embed-center iframe { max-width: 100%; border: 1px solid var(--line); border-radius: 8px; }
.legacy__body .union-example { white-space: pre; overflow-x: auto; font-family: var(--font-mono); font-size: 0.82rem; line-height: 2; background: var(--code-bg); border: 1px solid var(--line); border-left: 3px solid var(--accent); border-radius: var(--radius); padding: 14px 16px; color: var(--fg-2); }
.legacy__body .union-example .label { color: var(--fg-3); }
.legacy__body .gist { font-size: 0.8rem; max-width: 100%; overflow-x: auto; }
.legacy__body .gist .blob-wrapper { max-width: 100%; }
.about-author { display: flex; flex-wrap: wrap; gap: 24px; align-items: flex-start; }
.about-author__photo { width: 120px; height: 120px; object-fit: cover; border-radius: 12px; }
.about-author__list { list-style: none; padding: 0; margin: 0; flex: 1; min-width: 220px; }
.notfound { padding-top: 72px; padding-bottom: 72px; }
.notfound__links { list-style: none; padding: 0; margin: 24px 0 0; display: flex; flex-wrap: wrap; gap: 10px; }

/* print */
@media print {
  .site-header, .site-footer, .lesson-layout__side, .lesson-layout__toc, .tracer__controls, .complete, .pager, .toc-inline { display: none !important; }
  .js .tracer[data-ready] .tracer__step { display: flex !important; }
}