:root {
  color-scheme: light;
  --ink: #18212f;
  --muted: #5e6876;
  --paper: #f7f8fb;
  --panel: #ffffff;
  --line: #d9dee8;
  --teal: #007c89;
  --teal-soft: #d8f1f1;
  --violet: #5c4bb6;
  --amber: #f0ad2c;
  --coral: #d94f45;
  --green: #27855d;
  --shadow: 0 18px 44px rgba(24, 33, 47, 0.08);
  --radius: 8px;
  font-family: "Segoe UI", "Noto Sans TC", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  line-height: 1.6;
}

a {
  color: inherit;
}

button,
input,
select {
  font: inherit;
}

button {
  cursor: pointer;
}

.skip-link {
  background: var(--ink);
  color: #fff;
  left: 1rem;
  padding: 0.55rem 0.8rem;
  position: fixed;
  top: 0.75rem;
  transform: translateY(-140%);
  z-index: 20;
}

.skip-link:focus {
  transform: translateY(0);
}

.topbar {
  align-items: center;
  background: rgba(247, 248, 251, 0.94);
  border-bottom: 1px solid var(--line);
  display: flex;
  gap: 1.5rem;
  justify-content: space-between;
  min-height: 72px;
  padding: 0.8rem clamp(1rem, 4vw, 3rem);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: blur(14px);
}

.brand {
  align-items: center;
  display: inline-flex;
  gap: 0.8rem;
  text-decoration: none;
}

.brand-mark {
  align-items: center;
  background: var(--ink);
  border-radius: var(--radius);
  color: #fff;
  display: inline-flex;
  font-weight: 800;
  height: 42px;
  justify-content: center;
  width: 42px;
}

.brand-copy {
  display: grid;
  gap: 0.05rem;
}

.brand-copy strong {
  font-size: 1.05rem;
}

.brand-copy span {
  color: var(--muted);
  font-size: 0.85rem;
}

.topnav {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  justify-content: flex-end;
}

.topnav a,
.rail-list a {
  border-radius: var(--radius);
  color: var(--muted);
  font-size: 0.92rem;
  padding: 0.45rem 0.7rem;
  text-decoration: none;
}

.topnav a:hover,
.rail-list a:hover {
  background: #e9edf4;
  color: var(--ink);
}

.page-shell {
  display: grid;
  grid-template-columns: minmax(210px, 260px) minmax(0, 1fr);
  min-height: calc(100vh - 72px);
}

.rail {
  border-right: 1px solid var(--line);
  padding: 1.5rem clamp(1rem, 3vw, 2rem);
  position: sticky;
  top: 72px;
  height: calc(100vh - 72px);
  align-self: start;
}

.rail-block,
.rail-note {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1rem;
}

.rail-list {
  display: grid;
  gap: 0.35rem;
  list-style: decimal-leading-zero;
  margin: 0.7rem 0 0;
  padding-left: 1.3rem;
}

.rail-list li::marker {
  color: var(--teal);
  font-weight: 700;
}

.rail-list a {
  display: block;
  padding-inline: 0.25rem;
}

.rail-note {
  align-items: center;
  color: var(--muted);
  display: flex;
  font-size: 0.9rem;
  gap: 0.55rem;
  margin-top: 1rem;
}

.status-dot {
  background: var(--green);
  border-radius: 50%;
  box-shadow: 0 0 0 5px rgba(39, 133, 93, 0.14);
  display: inline-block;
  flex: 0 0 auto;
  height: 0.65rem;
  width: 0.65rem;
}

main {
  min-width: 0;
}

.section {
  border-bottom: 1px solid var(--line);
  padding: clamp(2rem, 5vw, 4.5rem) clamp(1rem, 5vw, 4.5rem);
}

.intro-grid {
  align-items: end;
  display: grid;
  gap: 1.5rem;
  grid-template-columns: minmax(0, 1.55fr) minmax(260px, 0.75fr);
  min-height: 430px;
}

.intro-copy h1 {
  font-size: clamp(2rem, 5vw, 4.5rem);
  line-height: 1.08;
  margin: 0.2rem 0 1rem;
  max-width: 920px;
}

.intro-copy h1 span {
  display: block;
}

.intro-copy .title-zh {
  font-size: 1em;
}

.intro-copy .title-en {
  font-size: 0.72em;
}

.intro-copy p {
  color: var(--muted);
  font-size: 1.08rem;
  max-width: 790px;
}

.eyebrow {
  color: var(--teal);
  font-size: 0.78rem;
  font-weight: 800;
  margin: 0;
  text-transform: uppercase;
}

.quick-panel {
  background: var(--ink);
  border-radius: var(--radius);
  color: #fff;
  display: grid;
  gap: 1px;
  overflow: hidden;
}

.quick-panel > div {
  background: rgba(255, 255, 255, 0.08);
  display: grid;
  gap: 0.2rem;
  padding: 1rem;
}

.metric-number {
  color: var(--amber);
  font-size: 2rem;
  font-weight: 800;
  line-height: 1;
}

.metric-label {
  color: rgba(255, 255, 255, 0.78);
  font-size: 0.92rem;
}

.section-heading {
  margin-bottom: 1.35rem;
  max-width: 820px;
}

.section-heading h2 {
  font-size: clamp(1.6rem, 3vw, 2.5rem);
  line-height: 1.18;
  margin: 0.2rem 0 0.5rem;
}

.section-heading p:not(.eyebrow) {
  color: var(--muted);
  margin: 0;
}

.chapter-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.chapter-card,
.practice-grid article,
.analysis-panel,
.visual-panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.chapter-card {
  display: grid;
  gap: 0.5rem;
  min-height: 190px;
  padding: 1rem;
  text-decoration: none;
  transition: border-color 140ms ease, box-shadow 140ms ease, transform 140ms ease;
}

.chapter-card:hover,
.chapter-card:focus-visible {
  border-color: #aeb8c8;
  box-shadow: 0 22px 52px rgba(24, 33, 47, 0.12);
  outline: none;
  transform: translateY(-2px);
}

.chapter-card .chapter-index {
  color: var(--teal);
  font-size: 0.78rem;
  font-weight: 800;
}

.chapter-card h3 {
  font-size: 1.05rem;
  line-height: 1.25;
  margin: 0;
}

.chapter-card p {
  color: var(--muted);
  font-size: 0.92rem;
  margin: 0;
}

.chapter-page {
  display: block;
}

.chapter-layout {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 1.15fr) minmax(300px, 0.85fr);
}

.chapter-hero {
  background: #fff;
}

.chapter-hero h1 {
  font-size: clamp(2rem, 5vw, 4rem);
  line-height: 1.08;
  margin: 0.25rem 0 0.8rem;
}

.chapter-hero p {
  color: var(--muted);
  max-width: 820px;
}

.chapter-panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1rem;
}

.chapter-panel h2,
.chapter-panel h3 {
  margin: 0 0 0.65rem;
}

.chapter-panel p,
.chapter-panel li {
  color: var(--muted);
}

.chapter-panel ul,
.chapter-panel ol {
  margin: 0;
  padding-left: 1.25rem;
}

.chapter-panel li + li {
  margin-top: 0.45rem;
}

.chapter-panel pre {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow-x: auto;
  padding: 0.7rem;
}

.chapter-panel pre code {
  background: transparent;
  padding: 0;
}

.chapter-actions {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-top: 1rem;
}

.text-link {
  align-items: center;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  display: inline-flex;
  font-weight: 800;
  min-height: 40px;
  padding: 0.45rem 0.7rem;
  text-decoration: none;
}

.text-link.primary {
  background: var(--teal);
  border-color: var(--teal);
  color: #fff;
}

.chapter-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: space-between;
}

.definition-panel {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.8rem;
  padding: 1rem;
}

.definition-formula {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  font-family: "Cambria Math", Georgia, serif;
  font-size: clamp(1.4rem, 4vw, 2.4rem);
  font-weight: 700;
  padding: 1rem;
  text-align: center;
}

.term-grid {
  display: grid;
  gap: 0.7rem;
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.term-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 0.85rem;
}

.term-card h3 {
  font-size: 0.98rem;
  margin: 0 0 0.35rem;
}

.term-card p {
  color: var(--muted);
  font-size: 0.9rem;
  margin: 0;
}

.term-example {
  background: #f5f8fa;
  border-left: 3px solid var(--teal);
  color: var(--muted);
  display: grid;
  gap: 0.15rem;
  margin-top: 0.7rem;
  padding: 0.55rem 0.65rem;
}

.term-example strong {
  color: var(--teal);
  font-size: 0.78rem;
}

.term-example span {
  font-size: 0.86rem;
  line-height: 1.55;
}

.tree-mini-svg,
.graph-mini-svg {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 220px;
  width: 100%;
}

.tree-mini-edge,
.graph-mini-edge {
  fill: none;
  stroke: #8792a1;
  stroke-linecap: round;
  stroke-width: 3;
}

.graph-mini-edge.directed {
  marker-end: url(#graph-mini-arrow);
}

.tree-mini-node,
.graph-mini-node {
  fill: var(--violet);
  stroke: #fff;
  stroke-width: 3;
}

.tree-mini-node.root,
.graph-mini-node.start {
  fill: var(--teal);
}

.tree-mini-node.leaf,
.graph-mini-node.target {
  fill: var(--coral);
}

.tree-mini-node.internal {
  fill: var(--amber);
}

.tree-mini-label,
.tree-mini-caption,
.graph-mini-label,
.graph-mini-weight {
  fill: #fff;
  font-weight: 900;
  text-anchor: middle;
}

.tree-mini-label,
.graph-mini-label {
  font-size: 16px;
}

.tree-mini-caption,
.graph-mini-weight {
  fill: var(--muted);
  font-size: 13px;
}

.konigsberg-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.konigsberg-figure {
  display: grid;
  gap: 0.45rem;
  margin: 0;
}

.konigsberg-figure figcaption {
  color: var(--ink);
  font-size: 0.92rem;
  font-weight: 900;
}

.konigsberg-map-svg {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 220px;
  width: 100%;
}

.konigsberg-water {
  fill: #b8dce8;
}

.konigsberg-land {
  fill: #cbdc9a;
  stroke: #91a66a;
  stroke-width: 2;
}

.konigsberg-land.island {
  fill: #d9e7ae;
}

.konigsberg-bridges rect {
  fill: #bf8257;
  stroke: #805337;
  stroke-width: 3;
}

.konigsberg-map-label {
  fill: #304435;
  font-size: 15px;
  font-weight: 900;
  text-anchor: middle;
}

.konigsberg-map-label.island {
  font-size: 14px;
}

.konigsberg-edge-summary {
  fill: var(--muted);
  font-size: 12px;
  font-weight: 900;
  text-anchor: middle;
}

.graph-example-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.graph-example-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.55rem;
  padding: 0.85rem;
}

.graph-example-card-source {
  border-color: var(--teal);
}

.graph-example-card h3 {
  font-size: 0.98rem;
  margin: 0;
}

.graph-example-card p {
  color: var(--muted);
  font-size: 0.88rem;
  margin: 0;
}

.graph-example-svg {
  background: #fbfcff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  width: 100%;
}

.graph-example-edge {
  fill: none;
  stroke: #8792a1;
  stroke-linecap: round;
  stroke-width: 3;
}

.graph-example-edge.directed {
  marker-end: url(#graph-example-arrow-directed);
}

.graph-example-node {
  fill: var(--violet);
  stroke: #fff;
  stroke-width: 3;
}

.graph-example-node.muted {
  fill: #a7b0bd;
}

.graph-example-label {
  fill: #fff;
  font-size: 15px;
  font-weight: 900;
  pointer-events: none;
  text-anchor: middle;
}

.graph-relation-svg {
  background: #fbfcff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  max-height: 245px;
  width: 100%;
}

.graph-example-edge.relation-active {
  stroke: var(--coral);
  stroke-width: 5;
}

.graph-relation-label,
.graph-relation-note {
  fill: var(--muted);
  font-size: 14px;
  font-weight: 900;
  text-anchor: middle;
}

.graph-relation-label.active {
  fill: var(--coral);
}

.graph-relation-note {
  font-size: 13px;
}

.representation-source-grid,
.weighted-representation-grid {
  align-items: center;
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 1fr) minmax(250px, 0.8fr);
}

.representation-diagram-grid {
  display: grid;
  gap: 0.9rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin-top: 1rem;
}

.representation-diagram-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.7rem;
  padding: 0.9rem;
}

.representation-diagram-card h3,
.representation-diagram-card p {
  margin: 0;
}

.representation-diagram-card h3 {
  font-size: 1rem;
}

.representation-diagram-card p {
  color: var(--muted);
  font-size: 0.9rem;
}

.matrix-example-table th,
.matrix-example-table td,
.weighted-edge-table th,
.weighted-edge-table td {
  text-align: center;
}

.matrix-hit {
  background: #dcefe9;
  color: #216856;
  font-weight: 900;
}

.adjacency-list-example,
.multilist-example {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: grid;
  gap: 0.55rem;
  padding: 0.7rem;
}

.adjacency-list-example > div {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 0.15rem;
}

.adjacency-list-example strong {
  min-width: 1.2rem;
}

.pointer-node {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 4px;
  color: var(--ink);
  font-size: 0.86rem;
  font-weight: 900;
  min-width: 2rem;
  padding: 0.3rem 0.45rem;
  text-align: center;
}

.multilist-heads,
.multilist-records {
  display: grid;
  gap: 0.4rem;
}

.multilist-heads span {
  color: var(--muted);
  font-family: Consolas, monospace;
  font-size: 0.84rem;
}

.multilist-records {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.multilist-records span {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 4px;
  display: grid;
  gap: 0.2rem;
  padding: 0.45rem;
  text-align: center;
}

.multilist-records small {
  color: var(--muted);
}

.edge-weight-label {
  fill: var(--coral);
  font-size: 15px;
  font-weight: 900;
  paint-order: stroke;
  stroke: #fff;
  stroke-width: 4px;
  text-anchor: middle;
}

.tree-diagram-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin-bottom: 1rem;
}

.tree-diagram-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.55rem;
  padding: 0.85rem;
}

.tree-diagram-card h3 {
  font-size: 1rem;
  margin: 0;
}

.tree-diagram-card p {
  color: var(--muted);
  margin: 0;
}

.tree-diagram-svg {
  background:
    linear-gradient(#eef2f7 1px, transparent 1px),
    linear-gradient(90deg, #eef2f7 1px, transparent 1px),
    #fbfcff;
  background-size: 28px 28px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 230px;
  width: 100%;
}

.tree-diagram-edge {
  stroke: #8b95a3;
  stroke-linecap: round;
  stroke-width: 2.5;
}

.tree-diagram-node {
  fill: var(--violet);
  stroke: #fff;
  stroke-width: 3;
}

.tree-diagram-node.root,
.tree-diagram-node.winner {
  fill: var(--teal);
}

.tree-diagram-node.internal {
  fill: var(--amber);
}

.tree-diagram-node.leaf {
  fill: var(--coral);
}

.tree-diagram-node.heap-max {
  fill: #e46053;
}

.tree-diagram-node.heap-min {
  fill: #4c9f70;
}

.tree-diagram-node.loser {
  fill: #5f6f89;
}

.tree-diagram-label,
.tree-diagram-note {
  font-weight: 900;
  pointer-events: none;
  text-anchor: middle;
}

.tree-diagram-label {
  fill: #fff;
  font-size: 14px;
}

.tree-diagram-note {
  fill: var(--muted);
  font-size: 12px;
}

.tree-diagram-note.strong {
  fill: var(--ink);
  font-size: 13px;
}

.tree-material-grid,
.graph-material-grid {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 0.9fr) minmax(360px, 1.1fr);
}

.tree-code-panel,
.graph-code-panel {
  background: #101827;
  border: 1px solid #202b3f;
  border-radius: var(--radius);
  overflow: hidden;
}

.tree-code-panel h3,
.graph-code-panel h3 {
  background: #172133;
  color: #fff;
  margin: 0;
  padding: 0.7rem 0.85rem;
}

.tree-code-panel pre,
.graph-code-panel pre {
  margin: 0;
  overflow-x: auto;
  padding: 0.9rem;
}

.tree-code-panel code,
.graph-code-panel code {
  background: transparent;
  color: #e7edf8;
  font-size: 0.85rem;
  padding: 0;
}

.standalone-code-panel {
  margin-top: 1rem;
}

.traversal-strip {
  display: grid;
  gap: 0.45rem;
}

.traversal-row {
  align-items: center;
  background: #f8fafc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: grid;
  gap: 0.55rem;
  grid-template-columns: 110px minmax(0, 1fr);
  padding: 0.55rem;
}

.traversal-row strong {
  color: var(--ink);
}

.traversal-row span {
  color: var(--muted);
  font-family: Consolas, "Cascadia Mono", monospace;
  overflow-x: auto;
  white-space: nowrap;
}

.teaching-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.algorithm-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.75rem;
  padding: 1rem;
}

.algorithm-card h3 {
  margin: 0;
}

.algorithm-card p {
  color: var(--muted);
  margin: 0;
}

.diagram-stage {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: grid;
  gap: 0.6rem;
  min-height: 132px;
  padding: 0.75rem;
}

.mini-array,
.bucket-row,
.heap-level,
.merge-row {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.cell,
.bucket {
  align-items: center;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 6px;
  display: inline-flex;
  font-weight: 800;
  justify-content: center;
  min-height: 34px;
  min-width: 34px;
  padding: 0.25rem 0.45rem;
}

.cell.active {
  background: var(--amber);
  border-color: #d99a18;
}

.cell.compare {
  background: #ffe6e3;
  border-color: #e4aaa4;
}

.cell.sorted {
  background: var(--teal-soft);
  border-color: #8fcaca;
}

.cell.pivot {
  background: var(--coral);
  border-color: var(--coral);
  color: #fff;
}

.diagram-arrow {
  color: var(--muted);
  font-weight: 900;
  padding: 0 0.2rem;
}

.diagram-note {
  color: var(--muted);
  font-size: 0.86rem;
  font-weight: 700;
}

.merge-recursive-svg {
  background: #ffffff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 360px;
  width: 100%;
}

.merge-box rect {
  fill: #cfeff2;
  stroke: #50616c;
  stroke-width: 1.6;
}

.merge-box text {
  fill: #0f1724;
  font-size: 20px;
  font-weight: 800;
  text-anchor: middle;
}

.merge-arrow {
  fill: none;
  stroke: #66717e;
  stroke-linecap: round;
  stroke-width: 1.5;
}

.merge-divider {
  stroke: var(--amber);
  stroke-linecap: round;
  stroke-width: 4;
}

.merge-caption {
  fill: var(--teal);
  font-size: 18px;
  font-weight: 900;
  text-anchor: middle;
}

.heap-tree-svg {
  background: #ffffff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 330px;
  width: 100%;
}

.heap-tree-edge {
  stroke: #6f7a86;
  stroke-linecap: round;
  stroke-width: 2;
}

.heap-tree-node {
  fill: #bfe6df;
  stroke: #3f6d68;
  stroke-width: 2;
}

.heap-tree-node.max {
  fill: #ffe1a8;
  stroke: #c18416;
}

.heap-tree-value {
  fill: #0f1724;
  font-size: 22px;
  font-weight: 900;
  text-anchor: middle;
}

.heap-tree-index {
  fill: #4e5967;
  font-size: 15px;
  font-weight: 900;
  text-anchor: middle;
}

.heap-array-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.heap-array-strip span {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 6px;
  display: inline-grid;
  gap: 0.1rem;
  min-width: 46px;
  padding: 0.3rem 0.4rem;
  text-align: center;
}

.heap-array-strip strong {
  color: var(--ink);
  font-size: 0.95rem;
}

.heap-array-strip small {
  color: var(--muted);
  font-weight: 800;
}

.heap-demo-panel {
  background: #f8fafc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: grid;
  gap: 0.75rem;
  padding: 0.75rem;
}

.heap-demo-header {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: space-between;
}

.heap-demo-header strong,
.heap-demo-header span {
  display: block;
}

.heap-demo-header span {
  color: var(--muted);
  font-size: 0.9rem;
}

.heap-demo-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.heap-demo-svg {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 320px;
  width: 100%;
}

.heap-demo-edge {
  stroke: #8b95a3;
  stroke-linecap: round;
  stroke-width: 2;
}

.heap-demo-edge.muted {
  opacity: 0.35;
}

.heap-demo-node {
  fill: #cfeff2;
  stroke: #4a6a73;
  stroke-width: 2;
}

.heap-demo-node.compare {
  fill: #ffe6e3;
  stroke: var(--coral);
}

.heap-demo-node.swap {
  fill: var(--amber);
  stroke: #a87500;
}

.heap-demo-node.sorted {
  fill: #dcebe4;
  stroke: var(--green);
}

.heap-demo-node.outside {
  opacity: 0.62;
}

.heap-demo-value {
  fill: var(--ink);
  font-size: 23px;
  font-weight: 900;
  text-anchor: middle;
}

.heap-demo-index {
  fill: var(--muted);
  font-size: 13px;
  font-weight: 900;
  text-anchor: middle;
}

.heap-demo-array {
  display: grid;
  gap: 0.35rem;
  grid-template-columns: repeat(10, minmax(42px, 1fr));
}

.heap-demo-cell {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 6px;
  display: grid;
  gap: 0.08rem;
  min-height: 54px;
  padding: 0.3rem 0.25rem;
  text-align: center;
}

.heap-demo-cell strong {
  color: var(--ink);
  font-size: 1rem;
}

.heap-demo-cell small {
  color: var(--muted);
  font-weight: 800;
}

.heap-demo-cell.compare {
  background: #ffe6e3;
  border-color: #e4aaa4;
}

.heap-demo-cell.swap {
  background: #fff2c8;
  border-color: #d9a21e;
}

.heap-demo-cell.sorted {
  background: #e4f2ea;
  border-color: #8fc8ab;
}

.heap-demo-metrics {
  grid-template-columns: 0.75fr 0.75fr 1fr 2fr;
}

.radix-pass-svg {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  min-height: 420px;
  width: 100%;
}

.radix-pass-stack {
  display: grid;
  gap: 0.75rem;
}

.radix-pass-explanation {
  background: #f8fafc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--muted);
  display: grid;
  gap: 0.2rem;
  padding: 0.65rem 0.75rem;
}

.radix-pass-explanation strong {
  color: var(--ink);
}

.radix-title {
  fill: var(--teal);
  font-size: 24px;
  font-weight: 900;
  text-anchor: middle;
}

.radix-cell rect,
.radix-bucket-cell rect {
  fill: #cfeff2;
  stroke: #50616c;
  stroke-width: 1.6;
}

.radix-cell text,
.radix-bucket-cell text {
  fill: #0f1724;
  font-size: 18px;
  font-weight: 900;
  text-anchor: middle;
}

.radix-label {
  fill: #0f1724;
  font-size: 15px;
  font-weight: 900;
  text-anchor: middle;
}

.radix-arrow {
  fill: none;
  stroke: #66717e;
  stroke-linecap: round;
  stroke-width: 1.5;
}

.radix-bucket-line {
  stroke: #9aa4b2;
  stroke-linecap: round;
  stroke-width: 1.4;
}

.radix-highlight {
  fill: rgba(240, 173, 44, 0.32);
}

.radix-note {
  fill: var(--muted);
  font-size: 14px;
  font-weight: 800;
  text-anchor: middle;
}

.radix-lab-panel {
  display: grid;
  gap: 1rem;
}

.radix-lab-summary {
  display: grid;
  gap: 0.65rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.radix-lab-summary div {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: grid;
  gap: 0.2rem;
  padding: 0.7rem;
}

.radix-lab-summary span,
.radix-array-zone .eyebrow {
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 900;
}

.radix-array-zone {
  display: grid;
  gap: 0.55rem;
}

.radix-array-zone .eyebrow {
  margin: 0;
}

.radix-array-row,
.radix-bucket-grid {
  display: grid;
  gap: 0.45rem;
  grid-template-columns: repeat(10, minmax(0, 1fr));
}

.radix-array-cell {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 5px;
  display: grid;
  gap: 0.15rem;
  min-width: 0;
  padding: 0.55rem 0.35rem;
  text-align: center;
}

.radix-array-cell.active,
.radix-bucket.active {
  background: #fff5d6;
  border-color: var(--amber);
}

.radix-array-cell small {
  color: var(--muted);
  font-size: 0.68rem;
}

.radix-bucket {
  background: #f8fafc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  min-height: 8.5rem;
  overflow: hidden;
}

.radix-bucket > strong {
  background: #edf0f6;
  display: block;
  padding: 0.45rem;
  text-align: center;
}

.radix-bucket div {
  display: grid;
  gap: 0.3rem;
  padding: 0.45rem;
}

.radix-bucket span,
.radix-bucket em {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 4px;
  color: var(--ink);
  font-size: 0.78rem;
  font-style: normal;
  font-weight: 800;
  padding: 0.28rem 0.15rem;
  text-align: center;
}

.radix-bucket span.active {
  background: #ffeaa6;
  border-color: var(--amber);
}

.radix-bucket em {
  background: transparent;
  border-color: transparent;
  color: var(--muted);
  font-weight: 700;
}

.bucket {
  align-items: stretch;
  flex-direction: column;
  min-width: 56px;
  overflow: hidden;
  padding: 0;
}

.bucket strong {
  background: var(--ink);
  color: #fff;
  display: block;
  font-size: 0.78rem;
  padding: 0.18rem 0.4rem;
  text-align: center;
}

.bucket span {
  display: block;
  min-height: 30px;
  padding: 0.3rem 0.4rem;
  text-align: center;
}

.code-grid {
  display: grid;
  gap: 1rem;
}

.graph-code-stack {
  display: grid;
  gap: 1rem;
}

.graph-code-pair {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(280px, 0.85fr) minmax(0, 1.15fr);
}

.graph-code-pair .lesson-block,
.graph-code-pair .code-panel {
  min-width: 0;
}

.code-panel {
  background: #101827;
  border: 1px solid #202b3f;
  border-radius: var(--radius);
  overflow: hidden;
}

.code-panel h3 {
  background: #172133;
  color: #fff;
  font-size: 0.98rem;
  margin: 0;
  padding: 0.7rem 0.85rem;
}

.code-panel pre {
  margin: 0;
  overflow-x: auto;
  padding: 0.9rem;
}

.code-panel code {
  background: transparent;
  color: #e7edf8;
  font-size: 0.86rem;
  padding: 0;
}

.sort-lesson-stack {
  display: grid;
  gap: 1rem;
}

.sort-lesson {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.sort-lesson-header {
  background: #f5f7fb;
  border-bottom: 1px solid var(--line);
  display: grid;
  gap: 0.45rem;
  padding: 1rem;
}

.sort-lesson-header h3 {
  font-size: clamp(1.35rem, 2.5vw, 2rem);
  margin: 0;
}

.sort-lesson-header p {
  color: var(--muted);
  margin: 0;
}

.complexity-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.25rem;
}

.complexity-strip span {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: #394354;
  font-size: 0.78rem;
  font-weight: 800;
  padding: 0.22rem 0.55rem;
}

.lesson-layout {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 0.92fr) minmax(360px, 1.08fr);
  padding: 1rem;
}

.lesson-column {
  display: grid;
  gap: 0.8rem;
  align-content: start;
}

.lesson-block {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 0.8rem;
}

.lesson-block h4 {
  margin: 0 0 0.55rem;
}

.lesson-block p,
.lesson-block li {
  color: var(--muted);
}

.lesson-block p,
.lesson-block ol,
.lesson-block ul {
  margin: 0;
}

.lesson-block ol,
.lesson-block ul {
  padding-left: 1.25rem;
}

.lesson-block li + li {
  margin-top: 0.35rem;
}

.lesson-code {
  background: #101827;
  border: 1px solid #202b3f;
  border-radius: var(--radius);
  overflow: hidden;
}

.lesson-code h4 {
  background: #172133;
  color: #fff;
  margin: 0;
  padding: 0.7rem 0.85rem;
}

.lesson-code pre {
  margin: 0;
  overflow-x: auto;
  padding: 0.9rem;
}

.lesson-code code {
  background: transparent;
  color: #e7edf8;
  font-size: 0.85rem;
  padding: 0;
}

.chapter-tags {
  align-self: end;
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.chapter-tags span,
.pill {
  background: #edf0f6;
  border-radius: 999px;
  color: #394354;
  font-size: 0.76rem;
  font-weight: 700;
  padding: 0.2rem 0.48rem;
}

.lab-section {
  background: #fff;
}

.lab-grid {
  display: grid;
  gap: 1rem;
}

.sorting-grid,
.tree-grid,
.graph-grid {
  grid-template-columns: minmax(0, 1.45fr) minmax(320px, 0.85fr);
}

.visual-panel,
.analysis-panel {
  padding: 1rem;
}

.toolbar {
  align-items: end;
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-bottom: 0.8rem;
}

.field {
  display: grid;
  gap: 0.22rem;
  min-width: 132px;
}

.field span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
}

.field input[type="text"],
.field select {
  background: #f8f9fc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  min-height: 40px;
  padding: 0.45rem 0.6rem;
}

.wide-field {
  flex: 1 1 340px;
}

.compact-field {
  min-width: 110px;
}

input[type="range"] {
  accent-color: var(--teal);
  min-height: 40px;
}

.icon-btn,
.tab {
  align-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: inline-flex;
  gap: 0.4rem;
  justify-content: center;
  min-height: 40px;
  padding: 0.45rem 0.7rem;
  transition: transform 140ms ease, border-color 140ms ease, background 140ms ease;
  white-space: nowrap;
}

.icon-btn {
  background: #fff;
  color: var(--ink);
}

.icon-btn svg {
  height: 1rem;
  width: 1rem;
}

.icon-btn:hover,
.tab:hover {
  border-color: #aeb8c8;
  transform: translateY(-1px);
}

.icon-btn.primary {
  background: var(--teal);
  border-color: var(--teal);
  color: #fff;
}

.algorithm-tabs,
.representation-toggle {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 0.6rem 0 0.85rem;
}

.tab {
  background: #f4f6fa;
  color: #3b4553;
  font-size: 0.88rem;
  font-weight: 700;
}

.tab.active {
  background: var(--ink);
  border-color: var(--ink);
  color: #fff;
}

.chart-surface,
.tree-surface,
.graph-surface {
  background:
    linear-gradient(#eef2f7 1px, transparent 1px),
    linear-gradient(90deg, #eef2f7 1px, transparent 1px),
    #fbfcff;
  background-size: 28px 28px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  display: block;
  overflow: hidden;
  width: 100%;
}

.chart-surface {
  aspect-ratio: 16 / 7;
  min-height: 280px;
}

.tree-surface,
.graph-surface {
  aspect-ratio: 16 / 8.8;
  min-height: 320px;
}

.metric-row {
  display: grid;
  gap: 0.55rem;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin-top: 0.8rem;
}

.metric-row div {
  background: #f3f5f9;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  min-width: 0;
  padding: 0.6rem;
}

.metric-row strong {
  display: block;
  font-size: 1rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.metric-row span {
  color: var(--muted);
  display: block;
  font-size: 0.78rem;
  font-weight: 800;
  margin-top: 0.1rem;
}

.analysis-panel h3 {
  font-size: 1.05rem;
  margin: 0 0 0.7rem;
}

.analysis-panel h3 + h3 {
  margin-top: 1rem;
}

.responsive-table {
  overflow-x: auto;
}

table {
  border-collapse: collapse;
  min-width: 100%;
}

th,
td {
  border-bottom: 1px solid var(--line);
  font-size: 0.86rem;
  padding: 0.55rem 0.45rem;
  text-align: left;
  vertical-align: top;
}

th {
  color: var(--muted);
  font-weight: 800;
}

tr.active-row {
  background: var(--teal-soft);
}

.insight-box {
  background: #f8f3df;
  border: 1px solid #ead99a;
  border-radius: var(--radius);
  color: #4d4121;
  font-size: 0.94rem;
  margin-top: 0.9rem;
  padding: 0.8rem;
}

.sequence-output,
.representation-output {
  background: #f5f7fb;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  min-height: 70px;
  overflow-x: auto;
  padding: 0.8rem;
}

.sequence-output {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.sequence-output span {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 999px;
  font-weight: 800;
  min-width: 2rem;
  padding: 0.2rem 0.45rem;
  text-align: center;
}

.tree-compare {
  display: grid;
  gap: 0.6rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.tree-compare > div {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 0.55rem;
}

.tree-compare span {
  color: var(--muted);
  display: block;
  font-size: 0.8rem;
  font-weight: 800;
  margin-bottom: 0.35rem;
}

.tree-compare svg {
  background: #fbfcff;
  border-radius: var(--radius);
  display: block;
  height: 160px;
  width: 100%;
}

.custom-tree-lab {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 1.45fr) minmax(320px, 0.85fr);
}

.custom-tree-workspace,
.custom-tree-side {
  min-width: 0;
}

.custom-tree-toolbar {
  align-items: end;
}

.custom-tree-canvas {
  background:
    linear-gradient(#eef2f7 1px, transparent 1px),
    linear-gradient(90deg, #eef2f7 1px, transparent 1px),
    #fbfcff;
  background-size: 28px 28px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  cursor: pointer;
  display: block;
  min-height: 420px;
  width: 100%;
}

.custom-tree-metrics {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.custom-tree-list {
  display: grid;
  gap: 0.45rem;
  margin-top: 0.5rem;
  max-height: 360px;
  overflow: auto;
  padding-right: 0.15rem;
}

.custom-tree-list p {
  color: var(--muted);
  margin: 0;
}

.custom-tree-list-item {
  align-items: center;
  background: #f7f9fc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  display: flex;
  justify-content: space-between;
  min-height: 42px;
  padding: 0.5rem 0.65rem;
  text-align: left;
}

.custom-tree-list-item:hover {
  border-color: #aeb8c8;
}

.custom-tree-list-item.active {
  background: var(--teal-soft);
  border-color: var(--teal);
}

.custom-tree-list-item strong {
  font-size: 0.95rem;
}

.custom-tree-list-item span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
  margin-left: 0.75rem;
}

.custom-graph-lab {
  display: grid;
  gap: 1rem;
  grid-template-columns: minmax(0, 1.45fr) minmax(320px, 0.85fr);
}

.custom-graph-workspace,
.custom-graph-side {
  min-width: 0;
}

.custom-graph-toolbar {
  align-items: end;
}

.custom-graph-canvas {
  background:
    linear-gradient(#eef2f7 1px, transparent 1px),
    linear-gradient(90deg, #eef2f7 1px, transparent 1px),
    #fbfcff;
  background-size: 28px 28px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  cursor: pointer;
  display: block;
  min-height: 420px;
  width: 100%;
}

.custom-graph-metrics {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.custom-graph-adjacency {
  min-height: 150px;
}

.custom-graph-edge-list {
  display: grid;
  gap: 0.45rem;
  margin-top: 0.5rem;
  max-height: 230px;
  overflow: auto;
  padding-right: 0.15rem;
}

.custom-graph-edge-list p {
  color: var(--muted);
  margin: 0;
}

.custom-graph-edge-item {
  align-items: center;
  background: #f7f9fc;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--ink);
  display: flex;
  justify-content: space-between;
  min-height: 42px;
  padding: 0.5rem 0.65rem;
  text-align: left;
}

.custom-graph-edge-item:hover {
  border-color: #aeb8c8;
}

.custom-graph-edge-item.active {
  background: var(--teal-soft);
  border-color: var(--teal);
}

.custom-graph-edge-item strong {
  font-size: 0.95rem;
}

.custom-graph-edge-item span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
  margin-left: 0.75rem;
}

.representation-output {
  font-family: Consolas, "Cascadia Mono", monospace;
  font-size: 0.86rem;
  white-space: pre;
}

.practice-grid {
  display: grid;
  gap: 0.8rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.practice-grid article {
  padding: 1rem;
}

.practice-grid h3 {
  margin: 0 0 0.45rem;
}

.practice-grid p {
  color: var(--muted);
  margin: 0;
}

code {
  background: #eef1f6;
  border-radius: 5px;
  color: #2c3340;
  font-family: Consolas, "Cascadia Mono", monospace;
  font-size: 0.92em;
  padding: 0.1rem 0.25rem;
}

.site-footer {
  color: var(--muted);
  font-size: 0.9rem;
  padding: 1.5rem clamp(1rem, 5vw, 4.5rem) 2.2rem;
}

.site-footer p {
  margin: 0.25rem 0;
}

.site-footer a {
  color: var(--teal);
  font-weight: 800;
}

.bar {
  transition: fill 120ms ease;
}

.bar-label {
  fill: var(--muted);
  font-size: 10px;
  font-weight: 700;
}

.tree-edge,
.graph-edge {
  stroke: #a8b1c1;
  stroke-linecap: round;
}

.tree-node,
.graph-node {
  fill: var(--violet);
  stroke: #fff;
  stroke-width: 2.5;
  filter: drop-shadow(0 5px 8px rgba(24, 33, 47, 0.18));
}

.node-label,
.edge-label {
  font-weight: 800;
  pointer-events: none;
  text-anchor: middle;
}

.node-label {
  fill: #fff;
  font-size: 13px;
}

.edge-label {
  fill: var(--muted);
  font-size: 12px;
}

.graph-edge.active,
.tree-edge.active {
  stroke: var(--coral);
  stroke-width: 4;
}

.graph-edge.selected {
  stroke: var(--green);
  stroke-width: 5;
}

.graph-node.visited {
  fill: var(--green);
}

.graph-node.frontier {
  fill: var(--amber);
}

.graph-node.current,
.tree-node.current {
  fill: var(--coral);
}

@media (max-width: 1120px) {
  .page-shell {
    grid-template-columns: 1fr;
  }

  .rail {
    display: none;
  }

  .sorting-grid,
  .tree-grid,
  .graph-grid,
  .custom-tree-lab,
  .custom-graph-lab,
  .tree-material-grid,
  .graph-material-grid,
  .konigsberg-grid,
  .graph-code-pair,
  .representation-source-grid,
  .weighted-representation-grid,
  .chapter-layout,
  .teaching-grid,
  .lesson-layout,
  .intro-grid {
    grid-template-columns: 1fr;
  }

  .chapter-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .graph-example-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 720px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
    gap: 0.8rem;
  }

  .topnav {
    justify-content: flex-start;
  }

  .section {
    padding-inline: 1rem;
  }

  .intro-grid {
    min-height: auto;
  }

  .chapter-grid,
  .practice-grid,
  .term-grid,
  .graph-example-grid,
  .representation-diagram-grid,
  .tree-diagram-grid,
  .tree-compare,
  .custom-tree-metrics,
  .custom-graph-metrics,
  .traversal-row,
  .metric-row,
  .heap-demo-metrics {
    grid-template-columns: 1fr;
  }

  .heap-demo-array {
    grid-template-columns: repeat(5, minmax(42px, 1fr));
  }

  .toolbar {
    align-items: stretch;
  }

  .field,
  .icon-btn {
    flex: 1 1 100%;
  }

  .radix-array-row,
  .radix-bucket-grid {
    grid-template-columns: repeat(5, minmax(0, 1fr));
  }

  .radix-bucket {
    min-height: 6.5rem;
  }

  .algorithm-tabs .tab,
  .representation-toggle .tab {
    flex: 1 1 44%;
  }

  .chart-surface,
  .tree-surface,
  .graph-surface,
  .custom-tree-canvas,
  .custom-graph-canvas {
    min-height: 260px;
  }
}