/* The one stylesheet. Tokens first, then layout, then the SVG visual
   vocabulary shared by every renderer. No frameworks, no fonts, no deps. */

:root {
  color-scheme: light dark;
  --bg: #f6f8fb;
  --panel: #ffffff;
  --panel-2: #eef2f7;
  --text: #18202e;
  --muted: #5d6b7d;
  --line: #d7dee8;
  --accent: #1769e0;
  --accent-soft: #e3edfb;
  --good: #178044;
  --good-soft: #ddf3e4;
  --warn: #b45309;
  --warn-soft: #fdedd7;
  --bad: #b42318;
  --bad-soft: #fbe1de;
  --cell-bg: #ffffff;
  --shadow: 0 1px 3px rgb(16 24 40 / 8%), 0 1px 2px rgb(16 24 40 / 6%);
  --radius: 10px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f141a;
    --panel: #171e26;
    --panel-2: #1d2630;
    --text: #e8eef5;
    --muted: #9fadbd;
    --line: #2b3644;
    --accent: #6ea8ff;
    --accent-soft: #1c2c45;
    --good: #4ade80;
    --good-soft: #15301f;
    --warn: #fbbf24;
    --warn-soft: #382a10;
    --bad: #f87171;
    --bad-soft: #3a1715;
    --cell-bg: #1d2630;
    --shadow: none;
  }
}

[data-theme="light"] {
  --bg: #f6f8fb; --panel: #ffffff; --panel-2: #eef2f7; --text: #18202e;
  --muted: #5d6b7d; --line: #d7dee8; --accent: #1769e0; --accent-soft: #e3edfb;
  --good: #178044; --good-soft: #ddf3e4; --warn: #b45309; --warn-soft: #fdedd7;
  --bad: #b42318; --bad-soft: #fbe1de; --cell-bg: #ffffff;
  --shadow: 0 1px 3px rgb(16 24 40 / 8%), 0 1px 2px rgb(16 24 40 / 6%);
}

[data-theme="dark"] {
  --bg: #0f141a; --panel: #171e26; --panel-2: #1d2630; --text: #e8eef5;
  --muted: #9fadbd; --line: #2b3644; --accent: #6ea8ff; --accent-soft: #1c2c45;
  --good: #4ade80; --good-soft: #15301f; --warn: #fbbf24; --warn-soft: #382a10;
  --bad: #f87171; --bad-soft: #3a1715; --cell-bg: #1d2630; --shadow: none;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  line-height: 1.55;
}

a { color: var(--accent); }
a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 3px; }
h1, h2, h3 { line-height: 1.2; }
html { scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }

.wrap { max-width: 1080px; margin: 0 auto; padding: 0 20px; }
.visually-hidden {
  position: absolute; width: 1px; height: 1px; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap;
}
.fine-print { color: var(--muted); font-size: 0.8rem; }

.skip-link {
  position: absolute; top: -100%; left: 16px; z-index: 999;
  background: var(--accent); color: #fff; padding: 8px 16px;
  border-radius: 0 0 8px 8px; text-decoration: none; font-weight: 600;
}
.skip-link:focus { top: 0; }

/* ------------------------------------------------------------- buttons */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 8px 14px;
  font-size: 0.92rem;
  cursor: pointer;
  text-decoration: none;
}
.btn:hover { border-color: var(--accent); }
.btn[aria-disabled="true"] {
  opacity: 0.6;
  cursor: not-allowed;
  pointer-events: none;
}
.btn-secondary {
  background: var(--panel-2);
}

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}
[data-theme="dark"] .btn-primary, .btn-primary { color: #fff; }

/* ---------------------------------------------------------------- home */

.site-header {
  background: var(--panel);
  border-bottom: 1px solid var(--line);
  padding: 36px 0 28px;
  margin-bottom: 26px;
}
.header-row { display: flex; justify-content: space-between; gap: 16px; align-items: start; }
.header-actions { display: flex; flex-wrap: wrap; gap: 8px; justify-content: flex-end; }
.site-header h1 { margin: 0 0 8px; font-size: 1.9rem; }
.site-header em { color: var(--accent); font-style: normal; }
.tagline { margin: 0; color: var(--muted); max-width: 56ch; }

.search-box input {
  width: 100%;
  padding: 13px 18px;
  font-size: 1.05rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel);
  color: var(--text);
  margin-bottom: 10px;
}
.search-box input:focus { outline: 2px solid var(--accent); border-color: transparent; }

.category h2 {
  font-size: 1.05rem;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 26px 0 12px;
}
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 14px;
}
.card {
  display: block;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 18px;
  text-decoration: none;
  color: var(--text);
  box-shadow: var(--shadow);
}
.card { transition: border-color 180ms, transform 180ms, box-shadow 180ms; }
.card:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: 0 4px 12px rgb(16 24 40 / 10%); }
.card:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.card h3 { margin: 0 0 6px; font-size: 1.05rem; color: var(--accent); }
.card p { margin: 0; font-size: 0.88rem; color: var(--muted); }
.empty-results { color: var(--muted); padding: 24px 4px; }

.curriculum-section,
.domain-section {
  margin: 28px 0 18px;
}
.curriculum-section h2,
.domain-section h2 {
  margin: 0 0 8px;
  font-size: 1.28rem;
}
.section-intro {
  max-width: 78ch;
  color: var(--muted);
  margin: 0 0 16px;
}
.track-grid,
.domain-grid {
  display: grid;
  gap: 14px;
}
.track-grid {
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}
.track-grid-compact {
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}
.domain-grid {
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}
.track-card,
.domain-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.track-card {
  padding: 18px 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.track-card h3,
.domain-card h3 {
  margin: 0;
  font-size: 1.08rem;
}
.track-meta,
.domain-count {
  margin: 0;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}
.track-summary,
.track-outcome,
.domain-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
}
.track-outcome {
  color: var(--text);
}
.track-modules {
  margin: 2px 0 0;
  padding-left: 20px;
  color: var(--muted);
  font-size: 0.88rem;
}
.track-modules li { margin: 5px 0; }
.track-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin: auto 0 0;
  padding-top: 4px;
}
.track-count {
  color: var(--muted);
  font-size: 0.82rem;
}
.track-prereq {
  margin: 0;
  color: var(--muted);
  font-size: 0.8rem;
}
.track-followups {
  margin: 0;
  color: var(--muted);
  font-size: 0.8rem;
}

.learning-path-panel {
  margin-top: 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px;
  background: color-mix(in oklab, var(--panel) 92%, var(--text) 8%);
}
.learning-path-state {
  margin: 6px 0 4px;
  font-size: 0.8rem;
  color: var(--muted);
}

.learning-path-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin: 8px 0;
}

.learning-path-node {
  font-size: 0.84rem;
  color: var(--text);
  text-decoration: none;
  padding: 6px 10px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: color-mix(in oklab, var(--panel) 95%, var(--accent) 5%);
}

.learning-path-node.current {
  font-weight: 700;
  border-color: var(--accent);
  background: color-mix(in oklab, var(--accent) 16%, var(--panel) 84%);
}

.learning-path-upcoming p {
  margin: 6px 0 2px;
}

.track-nav-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 8px;
}

.learning-path-note {
  margin: 8px 0 0;
  font-size: 0.85rem;
  line-height: 1.4;
  color: var(--muted);
}

.track-progress {
  display: grid;
  gap: 4px;
  margin: 2px 0 0;
}
.track-progress progress {
  width: 100%;
  height: 0.8rem;
  accent-color: var(--accent);
}
.track-progress span {
  color: var(--muted);
  font-size: 0.8rem;
}
.track-card-compact .track-outcome {
  display: none;
}
.domain-card {
  padding: 16px 18px;
  display: grid;
  gap: 8px;
}
.domain-use {
  color: var(--text) !important;
  font-size: 0.86rem !important;
}
.mini-link-list {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  color: var(--muted);
  font-size: 0.82rem;
}
.mini-link-list a,
.more-count {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--text);
  padding: 2px 9px;
  text-decoration: none;
}
.mini-link-list a:hover {
  border-color: var(--accent);
  color: var(--accent);
}
.more-count {
  color: var(--muted);
}
.all-topics {
  margin: 28px 0;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 0 18px 8px;
}
.all-topics > summary {
  cursor: pointer;
  padding: 16px 0;
  color: var(--accent);
  font-weight: 700;
}
.all-topics .category:first-of-type h2 {
  margin-top: 10px;
}

.about-card, .visitors-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px 24px;
  margin: 28px 0;
}
.about-card h2, .visitors-card h2 { margin-top: 0; font-size: 1.15rem; }
.visitors-card img { max-width: 100%; border-radius: 6px; }

.site-footer {
  border-top: 1px solid var(--line);
  margin-top: 30px;
  padding: 18px 20px 30px;
  text-align: center;
  color: var(--muted);
  font-size: 0.9rem;
}

/* ---------------------------------------------------------- topic page */

.topic-layout {
  display: grid;
  grid-template-columns: 230px 1fr;
  min-height: 100vh;
}
.topic-nav {
  border-right: 1px solid var(--line);
  background: var(--panel);
  padding: 18px 16px 30px;
  font-size: 0.9rem;
}
.topic-nav .home-link { display: block; margin-bottom: 10px; text-decoration: none; }
.topic-nav h2 {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--muted);
  margin: 16px 0 4px;
}
.topic-nav ul { list-style: none; margin: 0; padding: 0; }
.topic-nav a { display: block; padding: 3px 8px; border-radius: 6px; text-decoration: none; color: var(--text); }
.topic-nav a:hover { background: var(--panel-2); }
.topic-nav a[aria-current="page"] { background: var(--accent-soft); color: var(--accent); font-weight: 600; }

.topic-main { padding: 22px 26px 50px; min-width: 0; }
.topic-header h1 { margin: 0; font-size: 1.6rem; }
.topic-summary { color: var(--muted); margin: 6px 0 12px; max-width: 70ch; }
.topic-progress {
  margin: 2px 0 10px;
  color: var(--muted);
  font-size: 0.82rem;
}

.link-chips { margin-bottom: 14px; }
.chip-row { margin: 4px 0; display: flex; flex-wrap: wrap; gap: 6px; align-items: center; }
.chip-caption { font-size: 0.8rem; color: var(--muted); margin-right: 2px; }
.chip {
  display: inline-block;
  background: var(--accent-soft);
  color: var(--accent);
  border-radius: 999px;
  padding: 2px 12px;
  font-size: 0.82rem;
  text-decoration: none;
}
.chip:hover { outline: 1px solid var(--accent); }
.chip-more {
  color: var(--muted);
  background: var(--panel-2);
}
.chip[aria-current="true"] {
  outline: 1px solid var(--accent);
  font-weight: 700;
}

.topic-context {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 18px;
  margin: 0 0 12px;
}
.topic-context h2 {
  margin: 0 0 10px;
  font-size: 1rem;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}
.context-primary {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px 16px;
}
.context-primary h3,
.context-card h3 {
  margin: 0 0 6px;
  font-size: 1rem;
}
.context-primary p,
.context-card p {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 0.9rem;
}
.context-primary .context-use {
  color: var(--text);
}
.context-paths {
  margin-top: 10px;
}
.step-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 10px;
}
.step-nav a {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--accent);
  padding: 6px 10px;
  text-decoration: none;
  font-size: 0.88rem;
}
.step-nav a:hover {
  border-color: var(--accent);
}
.context-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 10px;
  margin-top: 10px;
}
.context-card {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 14px;
}

.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: end;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 10px;
}
.controls label { display: grid; gap: 4px; font-size: 0.82rem; color: var(--muted); }
.controls input, .controls select {
  padding: 8px 10px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--bg);
  color: var(--text);
  font-size: 0.95rem;
  min-width: 130px;
}
.controls input:focus, .controls select:focus { outline: 2px solid var(--accent); }

.error-box {
  background: var(--bad-soft);
  color: var(--bad);
  border-radius: 8px;
  padding: 10px 14px;
  margin: 0 0 10px;
}

/* Unified animation stage: explanation text + SVG in one card. */
.learn-grid { display: flex; flex-direction: column; gap: 12px; }

.vis-stage {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
}
.vis-explanation {
  padding: 18px 22px 10px;
  border-bottom: 1px solid var(--line);
  background:
    linear-gradient(180deg, var(--accent-soft) 0%, transparent 100%);
}
.vis-panel {
  padding: 14px;
  min-height: 240px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.vis-panel svg {
  width: min(100%, 860px);
  height: auto;
  max-height: 54vh;
}
.vis-panel [data-id] {
  animation: viz-reveal 260ms ease-out both;
}

.frame-log-panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 16px;
}
.learn-tools {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 8px;
  gap: 10px;
}
.study-control {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--muted);
  font-size: 0.82rem;
  cursor: pointer;
}
.frame-log {
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  margin: 4px 0 0;
}
.frame-log-title {
  margin: 0 0 8px;
  font-size: 0.85rem;
  color: var(--text);
}
.frame-log-list {
  margin: 0 0 0 18px;
  padding: 0;
  max-height: 116px;
  overflow-y: auto;
  overflow-x: hidden;
}
.frame-log-item {
  margin: 0 0 6px;
  font-size: 0.75rem;
  color: var(--muted);
  line-height: 1.35;
}
.frame-log-item.active {
  color: var(--accent);
  font-weight: 700;
}
.explanation {
  font-size: 1.12rem;
  line-height: 1.6;
  min-height: 2.4em;
  margin: 0 0 6px;
  max-width: 85ch;
}
.invariant {
  font-size: 0.88rem;
  color: var(--accent);
  background: var(--accent-soft);
  border-radius: 8px;
  padding: 8px 12px;
  margin: 0 0 4px;
  max-width: fit-content;
}

/* SVG annotation badges rendered on highlighted elements */
.svg-annotation {
  font-size: 11px;
  font-weight: 700;
  text-anchor: middle;
  dominant-baseline: central;
  pointer-events: none;
}
.svg-anno-bg {
  rx: 4;
  ry: 4;
}
.anno-compare .svg-anno-bg { fill: var(--warn); }
.anno-compare .svg-annotation { fill: #fff; }
.anno-swap .svg-anno-bg { fill: var(--bad); }
.anno-swap .svg-annotation { fill: #fff; }
.anno-found .svg-anno-bg { fill: var(--good); }
.anno-found .svg-annotation { fill: #fff; }
.anno-active .svg-anno-bg { fill: var(--accent); }
.anno-active .svg-annotation { fill: #fff; }
.anno-sorted .svg-anno-bg { fill: var(--good-soft); stroke: var(--good); stroke-width: 1; }
.anno-sorted .svg-annotation { fill: var(--good); }
.anno-pivot .svg-anno-bg { fill: var(--accent-soft); stroke: var(--accent); stroke-width: 1; }
.anno-pivot .svg-annotation { fill: var(--accent); }
.player-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 22px;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--line);
  padding-top: 12px;
}
.player-controls { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.speed-label { font-size: 0.82rem; color: var(--muted); display: inline-flex; gap: 6px; align-items: center; }
.progress-area { flex: 1 1 220px; max-width: 380px; }
.export-area { display: flex; gap: 8px; align-items: center; }
.progress-text { margin: 0 0 2px; font-size: 0.82rem; color: var(--muted); }
.step-slider { width: 100%; accent-color: var(--accent); }

/* study notes under the animation */
.study {
  margin-top: 18px;
  max-width: none;
}
.study-title {
  font-size: 1.35rem;
  border-bottom: 1px solid var(--line);
  padding-bottom: 10px;
  margin-bottom: 10px;
}
.study-jump-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 0 0 14px;
}
.study-jump-list a {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--accent);
  font-size: 0.84rem;
  padding: 4px 11px;
  text-decoration: none;
}
.study-jump-list a:hover {
  border-color: var(--accent);
}
.study-sections {
  display: flex;
  flex-direction: column;
  gap: 14px;
  width: 100%;
}
.study-section {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 22px;
  box-shadow: var(--shadow);
  width: 100%;
  min-width: 0;
}
.study-section summary {
  cursor: pointer;
  list-style: none;
}
.study-section summary::-webkit-details-marker {
  display: none;
}
.study-section-body {
  margin-top: 10px;
  max-width: 90ch;
  margin-left: auto;
  margin-right: auto;
}
.study-section h3 {
  font-size: 1.08rem;
  margin: 0 0 10px;
  color: var(--accent);
}
.study-section p {
  margin: 9px 0;
  line-height: 1.68;
}
.study-list {
  margin: 8px 0 0 18px;
  padding: 0;
}
.study-list li {
  margin: 8px 0;
  line-height: 1.6;
}

.study-quote {
  margin: 16px 0;
  padding: 12px 20px;
  border-left: 4px solid var(--accent, #4fc3f7);
  background: rgba(79, 195, 247, 0.06);
  border-radius: 0 6px 6px 0;
}
.study-quote p {
  margin: 0;
  font-style: italic;
  line-height: 1.6;
}
.study-quote cite {
  display: block;
  margin-top: 8px;
  font-style: normal;
  font-size: 0.9em;
  opacity: 0.8;
}

.study-table {
  margin: 16px 0;
  border-collapse: collapse;
  font-size: 0.92em;
  max-width: 100%;
  overflow-x: auto;
  display: block;
}
.study-table th,
.study-table td {
  padding: 8px 14px;
  text-align: left;
  border-bottom: 1px solid rgba(255,255,255,0.1);
}
.study-table th {
  font-weight: 600;
  background: rgba(255,255,255,0.04);
  position: sticky;
  top: 0;
}
.study-table tr:hover td {
  background: rgba(79, 195, 247, 0.04);
}

.study-code {
  margin: 16px 0;
  padding: 14px 18px;
  background: rgba(0,0,0,0.3);
  border-radius: 6px;
  overflow-x: auto;
  font-size: 0.88em;
  line-height: 1.5;
}
.study-code code {
  font-family: 'Fira Code', 'JetBrains Mono', 'Consolas', monospace;
}

.study-diagram {
  margin: 16px 0;
  padding: 14px 18px;
  background: rgba(0,0,0,0.2);
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: 6px;
  font-family: 'Fira Code', 'Consolas', monospace;
  font-size: 0.85em;
  line-height: 1.4;
  overflow-x: auto;
  white-space: pre;
}

.study-note {
  margin: 16px 0;
  padding: 12px 18px;
  background: rgba(255, 183, 77, 0.08);
  border-left: 4px solid rgba(255, 183, 77, 0.6);
  border-radius: 0 6px 6px 0;
}
.study-note-label {
  display: block;
  margin-bottom: 4px;
  font-size: 0.85em;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: rgba(255, 183, 77, 0.9);
}
.study-note p {
  margin: 0;
  line-height: 1.6;
}

.study-image {
  margin: 24px 0;
}
.study-image img {
  width: 100%;
  max-width: 100%;
  height: auto;
  border-radius: 8px;
  border: 1px solid rgba(255,255,255,0.08);
}
.study-image figcaption {
  margin-top: 8px;
  font-size: 0.88em;
  opacity: 0.7;
  line-height: 1.5;
  text-align: center;
}

.study-callout {
  margin: 20px 0;
  padding: 16px 20px;
  background: rgba(79, 195, 247, 0.06);
  border: 1px solid rgba(79, 195, 247, 0.2);
  border-radius: 8px;
}
.study-callout p {
  margin: 0;
  font-weight: 600;
  font-size: 1.05em;
  line-height: 1.6;
}

.study-copy-btn {
  display: inline-block;
  margin: 12px 0;
  padding: 8px 18px;
  background: rgba(79, 195, 247, 0.12);
  color: var(--accent, #4fc3f7);
  border: 1px solid rgba(79, 195, 247, 0.3);
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.88em;
  font-weight: 500;
  transition: background 0.2s, border-color 0.2s;
}
.study-copy-btn:hover {
  background: rgba(79, 195, 247, 0.22);
  border-color: rgba(79, 195, 247, 0.5);
}

@media (max-width: 880px) {
  .topic-layout { grid-template-columns: 1fr; }
  .topic-nav { display: none; }
}

@media (max-width: 600px) {
  body { overflow-x: hidden; }
  .topic-layout {
    width: 100%;
    max-width: 100vw;
    min-width: 0;
  }
  .topic-header,
  .topic-context,
  .learn-grid {
    width: 100%;
    max-width: 100%;
    min-width: 0;
  }
  .topic-main {
    width: 100%;
    max-width: 100vw;
    padding: 22px 14px 42px;
    overflow-x: hidden;
  }
  .header-row {
    display: block;
  }
  .header-row .btn {
    margin-top: 10px;
    padding: 7px 10px;
  }
  .topic-header h1 {
    width: 362px;
    max-width: 100%;
    font-size: 1.34rem;
    line-height: 1.22;
    white-space: normal;
    overflow-wrap: break-word;
    word-break: normal;
  }
  .topic-summary,
  .topic-progress,
  .explanation,
  .invariant,
  .study p,
  .chip,
  .track-card,
  .domain-card,
  .context-card {
    max-width: 100%;
    overflow-wrap: anywhere;
  }
  .topic-summary {
    width: 362px;
    max-width: 362px;
  }
  .explanation,
  .invariant {
    width: 100%;
    max-width: 100%;
    white-space: normal;
    word-break: break-word;
  }
  .chip-row {
    width: 362px;
    max-width: 362px;
  }
  .chip-row,
  .context-grid,
  .step-nav,
  .player-bar,
  .player-controls,
  .export-area,
  .speed-label {
    min-width: 0;
    max-width: 100%;
  }
  .invariant {
    max-width: 100%;
  }
  .controls,
  .topic-context,
  .vis-stage,
  .vis-panel,
  .frame-log-panel,
  .study {
    width: 100%;
    min-width: 0;
    max-width: 100%;
  }
  .study {
    width: 100%;
    max-width: 100%;
    overflow-x: hidden;
  }
  .study p,
  .study a {
    min-width: 0;
    max-width: 100%;
    overflow-wrap: anywhere;
    word-break: normal;
  }
  .frame-log-list {
    max-height: 94px;
  }
  .learn-tools {
    flex-direction: column;
    align-items: flex-start;
  }
  .controls {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    align-items: stretch;
  }
  .controls label {
    min-width: 0;
  }
  .controls input,
  .controls select {
    width: 100%;
    min-width: 0;
  }
  .controls .btn {
    justify-self: start;
  }
  .track-grid,
  .domain-grid,
  .context-grid {
    grid-template-columns: minmax(0, 1fr);
  }
  .study-section {
    padding: 16px 14px;
  }
  .track-actions,
  .step-nav {
    align-items: stretch;
  }
  .player-bar { justify-content: flex-start; }
  .player-controls,
  .export-area {
    width: 100%;
  }
  .progress-area {
    flex-basis: 100%;
    max-width: 100%;
    min-width: 0;
  }
  .step-slider {
    width: calc(100% - 4px);
    min-width: 0;
  }
  .vis-panel {
    padding: 8px;
    overflow-x: auto;
    overflow-y: hidden;
    justify-content: center;
  }
  .vis-panel svg {
    width: 100%;
    max-width: 620px;
    max-height: none;
    flex: 0 0 auto;
    display: block;
  }
}

/* -------------------------------------------- SVG visual vocabulary */

svg text {
  font-family: ui-monospace, "Cascadia Mono", Consolas, monospace;
  font-size: 16px;
  fill: var(--text);
}
.svg-center { text-anchor: middle; dominant-baseline: central; }
.svg-center-y { dominant-baseline: central; }
.svg-right { text-anchor: end; }
.svg-small { font-size: 12.5px; }
.svg-muted { fill: var(--muted); }
.svg-label { fill: var(--muted); font-size: 13px; }
.svg-link { stroke: var(--muted); stroke-width: 2; }
.svg-arrowhead { fill: var(--muted); }
.svg-bracket { fill: none; stroke: var(--line); stroke-width: 3; }

/* Depth pass: every cell floats with a soft shadow; the semantic highlight
   states glow and pulse so the eye is pulled exactly where the algorithm is
   working. Stunning, but never at the cost of follow-along clarity. */
.cell rect, .cell circle {
  fill: var(--cell-bg);
  stroke: var(--line);
  stroke-width: 2;
  transition: fill 250ms, stroke 250ms, opacity 250ms, filter 250ms;
  filter: drop-shadow(0 2.5px 2px rgb(10 20 40 / 22%));
}

@keyframes pulse-active {
  0%, 100% { filter: drop-shadow(0 0 2px var(--accent)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
  50% { filter: drop-shadow(0 0 9px var(--accent)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
}
@keyframes pulse-good {
  0%, 100% { filter: drop-shadow(0 0 2px var(--good)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
  50% { filter: drop-shadow(0 0 10px var(--good)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
}
@keyframes pulse-bad {
  0%, 100% { filter: drop-shadow(0 0 2px var(--bad)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
  50% { filter: drop-shadow(0 0 9px var(--bad)) drop-shadow(0 2px 2px rgb(10 20 40 / 20%)); }
}
@keyframes viz-reveal {
  from { opacity: 0.32; }
  to { opacity: 1; }
}
@keyframes edge-flow {
  to { stroke-dashoffset: -32; }
}
.hl-active rect, .hl-active circle { animation: pulse-active 1.6s ease-in-out infinite; }
.hl-found rect, .hl-found circle { animation: pulse-good 1.8s ease-in-out infinite; }
.hl-swap rect, .hl-swap circle { animation: pulse-bad 1.2s ease-in-out infinite; }
.mcell.hl-active rect, .plot-marker.hl-active circle, .pt.hl-compare circle,
.centroid.hl-active circle, .edge.hl-found line {
  animation: pulse-active 1.6s ease-in-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .cell rect, .cell circle, .mcell rect, .plot-marker circle, .pt circle,
  .centroid circle, .edge line, .vis-panel [data-id] { animation: none !important; }
}
.cell .bucket-empty { fill: var(--bg); stroke-dasharray: 4 4; }

/* semantic highlight states (set per-step by the renderers) */
.hl-active rect, .hl-active circle { stroke: var(--accent); stroke-width: 3.5; }
.hl-compare rect, .hl-compare circle { fill: var(--warn-soft); stroke: var(--warn); }
.hl-swap rect, .hl-swap circle { fill: var(--bad-soft); stroke: var(--bad); }
.hl-sorted rect, .hl-sorted circle { fill: var(--good-soft); stroke: var(--good); }
.hl-found rect, .hl-found circle { fill: var(--good-soft); stroke: var(--good); stroke-width: 3.5; }
.hl-range rect, .hl-range circle { fill: var(--accent-soft); }
.hl-visited rect, .hl-visited circle { opacity: 0.45; }
.hl-removed rect, .hl-removed circle { opacity: 0.35; stroke-dasharray: 5 5; stroke: var(--bad); }
.hl-pivot rect, .hl-pivot circle { fill: var(--accent-soft); stroke: var(--accent); stroke-width: 3; }
.hl-collision rect { fill: var(--bad-soft); stroke: var(--bad); }
.hl-returning rect { stroke: var(--good); stroke-width: 3.5; }

/* call-tree frame status */
.ct-active rect { stroke: var(--accent); stroke-width: 3; }
.ct-waiting rect { opacity: 0.75; }
.ct-returned rect { fill: var(--good-soft); stroke: var(--good); }
.ct-returned text { fill: var(--text); }

/* plot + scatter */
:root, [data-theme="light"], [data-theme="dark"] {
  --viz-0: #2f7de1;
  --viz-1: #d97706;
  --viz-2: #0a9b6c;
  --viz-3: #d6409f;
}
.svg-axis { stroke: var(--muted); stroke-width: 1.5; }
.series polyline { fill: none; stroke-width: 2.5; }
.s-0 polyline, .s-0 text { stroke: var(--viz-0); }
.s-1 polyline, .s-1 text { stroke: var(--viz-1); }
.s-2 polyline, .s-2 text { stroke: var(--viz-2); }
.s-3 polyline, .s-3 text { stroke: var(--viz-3); }
.series text { stroke: none; fill: var(--text); }
.series.hl-active polyline { stroke-width: 4.5; }
.series.hl-visited polyline { opacity: 0.3; }
.vector line { stroke: var(--bad); stroke-width: 2.5; }
.vector-arrowhead { fill: var(--bad); }
.plot-marker circle { fill: var(--accent); stroke: var(--panel); stroke-width: 2; }
.plot-marker.hl-visited circle { opacity: 0.35; }
.pt circle { stroke: var(--panel); stroke-width: 1.5; }
.cluster-none circle { fill: var(--muted); }
.cluster-0 circle { fill: var(--viz-0); }
.cluster-1 circle { fill: var(--viz-1); }
.cluster-2 circle { fill: var(--viz-2); }
.cluster-3 circle { fill: var(--viz-3); }
.pt.hl-compare circle { stroke: var(--warn); stroke-width: 3; }
.centroid circle { fill: none; stroke-width: 3.5; }
.centroid line { stroke-width: 2.5; }
.centroid.cluster-0 :is(circle, line) { stroke: var(--viz-0); }
.centroid.cluster-1 :is(circle, line) { stroke: var(--viz-1); }
.centroid.cluster-2 :is(circle, line) { stroke: var(--viz-2); }
.centroid.cluster-3 :is(circle, line) { stroke: var(--viz-3); }
.centroid.hl-active circle { stroke-dasharray: 5 4; }

/* graph */
.edge line { stroke: var(--line); stroke-width: 2.5; }
.edge-weight-bg { fill: var(--panel); stroke: var(--line); stroke-width: 1; }
.edge.hl-active line {
  stroke: var(--accent);
  stroke-width: 4;
  stroke-dasharray: 10 7;
  animation: edge-flow 950ms linear infinite;
}
.edge.hl-compare line { stroke: var(--warn); stroke-width: 4; }
.edge.hl-found line {
  stroke: var(--good);
  stroke-width: 4.5;
  stroke-dasharray: 12 6;
  animation: edge-flow 1100ms linear infinite, pulse-good 1.8s ease-in-out infinite;
}
.edge.hl-visited line { opacity: 0.35; }

/* matrix */
.mcell rect {
  fill: var(--accent);
  stroke: var(--line);
  stroke-width: 1;
  transition: fill-opacity 200ms, stroke 220ms, filter 220ms;
}
.mcell text { fill: var(--text); }
.mcell.hl-active rect {
  stroke: var(--accent);
  stroke-width: 3;
  filter: drop-shadow(0 0 8px var(--accent));
}
.mcell.hl-compare rect {
  stroke: var(--warn);
  stroke-width: 3;
  filter: drop-shadow(0 0 7px var(--warn));
}
.mlabel.hl-active text { fill: var(--accent); font-weight: 700; }
.mlabel.hl-compare text { fill: var(--warn); font-weight: 700; }

/* Inline topic cross-links inside explanations and study notes */
.inline-topic-link {
  color: var(--accent, #6ea8fe);
  text-decoration: underline;
  text-decoration-style: dotted;
  text-underline-offset: 2px;
  font-weight: 600;
}
.inline-topic-link:hover {
  text-decoration-style: solid;
}

.external-source-link {
  color: var(--accent);
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
  overflow-wrap: anywhere;
}

/* Print: students should be able to print study notes cleanly */
@media print {
  .site-header, .site-footer, .topic-nav, .controls,
  .player-bar, .vis-stage, .search-box, .frame-log-panel,
  .track-actions, .export-area, .skip-link { display: none !important; }
  .topic-layout { display: block; }
  .topic-main { padding: 0; }
  .study-section { break-inside: avoid; box-shadow: none; border: 1px solid #ccc; }
  .study-section[open] { display: block; }
  body { background: #fff; color: #000; font-size: 11pt; }
  a { color: #000; text-decoration: underline; }
  .study-jump-list a::after { content: " (#" attr(href) ")"; font-size: 0.8em; }
}