:root {
  --bg: #0f1420;
  --panel: #161d2e;
  --panel-2: #1c2438;
  --border: #2a3450;
  --text: #e8ecf5;
  --muted: #8792ab;
  --accent: #5b9dff;
  --accent-2: #ffb454;
  --good: #52d68a;
  --bad: #ff6b7a;
  --dim: #3a4360;
  --code-bg: #0c1120;
  --code-line-active: #24314f;
  --radius: 10px;
  --mono: 'SF Mono', 'Fira Code', Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Inter, Roboto, sans-serif;
}

:root[data-theme="light"] {
  --bg: #f4f6fb;
  --panel: #ffffff;
  --panel-2: #eef1f8;
  --border: #dbe1ef;
  --text: #1a2033;
  --muted: #626b85;
  --accent: #2f6fed;
  --accent-2: #c97a12;
  --good: #1f9d5c;
  --bad: #d7414f;
  --dim: #c7cee2;
  --code-bg: #eef1f8;
  --code-line-active: #dce6ff;
}

@media (prefers-color-scheme: light) {
  :root:not([data-theme="dark"]) {
    --bg: #f4f6fb;
    --panel: #ffffff;
    --panel-2: #eef1f8;
    --border: #dbe1ef;
    --text: #1a2033;
    --muted: #626b85;
    --accent: #2f6fed;
    --accent-2: #c97a12;
    --good: #1f9d5c;
    --bad: #d7414f;
    --dim: #c7cee2;
    --code-bg: #eef1f8;
    --code-line-active: #dce6ff;
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
}

body {
  display: grid;
  grid-template-columns: 260px 1fr 380px;
  grid-template-rows: 100vh;
  overflow: hidden;
}

/* ---------------------------------------------------------------- Sidebar */
.sidebar {
  background: var(--panel);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  padding: 16px 10px;
}
.sidebar h1 {
  font-size: 15px;
  font-weight: 700;
  margin: 4px 8px 2px;
}
.sidebar .subtitle {
  font-size: 11.5px;
  color: var(--muted);
  margin: 0 8px 16px;
  line-height: 1.4;
}
.pattern-nav {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 3px;
}
.pattern-nav button {
  width: 100%;
  text-align: left;
  background: transparent;
  border: 1px solid transparent;
  color: var(--text);
  padding: 9px 10px;
  border-radius: 8px;
  cursor: pointer;
  font-size: 13px;
  display: flex;
  align-items: center;
  gap: 9px;
  transition: background .15s ease, border-color .15s ease;
}
.pattern-nav button:hover { background: var(--panel-2); }
.pattern-nav button.active {
  background: var(--panel-2);
  border-color: var(--border);
  color: var(--accent);
  font-weight: 600;
}
.pattern-nav .num {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  min-width: 20px;
}
.pattern-nav button.active .num { color: var(--accent); }

/* ------------------------------------------------------------------ Main */
.main {
  display: flex;
  flex-direction: column;
  min-width: 0;
  border-right: 1px solid var(--border);
}
.main-header {
  padding: 18px 24px 14px;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}
.main-header .kicker {
  font-size: 11px;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 700;
  margin-bottom: 4px;
}
.main-header h2 {
  margin: 0 0 6px;
  font-size: 20px;
}
.main-header .problem {
  font-size: 13px;
  color: var(--muted);
  line-height: 1.5;
  max-width: 70ch;
}
.main-header .meta-row {
  margin-top: 8px;
  display: flex;
  gap: 16px;
  font-size: 11.5px;
  color: var(--muted);
  font-family: var(--mono);
}
.main-header .meta-row b { color: var(--text); }

.stage-wrap {
  flex: 1;
  overflow: auto;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  min-height: 0;
}
.stage {
  width: 100%;
  max-width: 900px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 18px;
}
.stage .caption {
  font-size: 12px;
  color: var(--muted);
  text-align: center;
}
.stage .note {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--accent-2);
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 6px 12px;
  text-align: center;
}

.narration-bar {
  flex-shrink: 0;
  border-top: 1px solid var(--border);
  padding: 14px 24px;
  background: var(--panel);
}
.narration-bar .step-label {
  font-size: 10.5px;
  color: var(--muted);
  font-family: var(--mono);
  margin-bottom: 4px;
}
.narration-bar .narration-text {
  font-size: 15px;
  line-height: 1.5;
  min-height: 24px;
}

.controls {
  flex-shrink: 0;
  border-top: 1px solid var(--border);
  background: var(--panel);
  padding: 10px 24px 16px;
}
.progress-track {
  height: 4px;
  border-radius: 2px;
  background: var(--dim);
  overflow: hidden;
  margin-bottom: 12px;
  cursor: pointer;
}
.progress-fill {
  height: 100%;
  background: var(--accent);
  transition: width .25s ease;
}
.controls-row {
  display: flex;
  align-items: center;
  gap: 10px;
}
.controls-row .spacer { flex: 1; }
.ctrl-btn {
  background: var(--panel-2);
  border: 1px solid var(--border);
  color: var(--text);
  width: 36px;
  height: 36px;
  border-radius: 8px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  transition: background .15s ease, transform .1s ease;
}
.ctrl-btn:hover { background: var(--code-line-active); }
.ctrl-btn:active { transform: scale(.94); }
.ctrl-btn.play {
  width: 46px;
  height: 46px;
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  font-size: 16px;
}
.ctrl-btn.play:hover { filter: brightness(1.08); }
.speed-select {
  background: var(--panel-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 8px 10px;
  font-size: 12.5px;
  font-family: var(--mono);
  cursor: pointer;
}
.step-counter {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--muted);
  min-width: 70px;
  text-align: right;
}
.hint {
  font-size: 10.5px;
  color: var(--muted);
  font-family: var(--mono);
}

/* -------------------------------------------------------------- Code panel */
.code-panel {
  background: var(--code-bg);
  overflow-y: auto;
  padding: 18px 0;
}
.code-panel .code-title {
  font-size: 10.5px;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--muted);
  padding: 0 18px 10px;
  font-weight: 700;
}
.code-line {
  font-family: var(--mono);
  font-size: 12.5px;
  line-height: 1.65;
  white-space: pre;
  padding: 1px 18px 1px 14px;
  border-left: 3px solid transparent;
  color: var(--muted);
  transition: background .3s ease, color .3s ease, border-color .3s ease;
}
.code-line.active {
  background: var(--code-line-active);
  border-left-color: var(--accent);
  color: var(--text);
  font-weight: 600;
}

/* ----------------------------------------------------------- Shared primitives */
.track { display: flex; flex-direction: column; align-items: center; gap: 6px; }
.track.vertical { flex-direction: row; align-items: flex-start; gap: 28px; }
.track-row { display: flex; gap: 8px; }
.track.vertical .track-row { flex-direction: column-reverse; }
.pointer-row { position: relative; width: 100%; height: 28px; }
.chip {
  --slot-w: 52px;
  width: var(--slot-w);
  height: var(--slot-w);
  border-radius: 10px;
  background: var(--panel-2);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 15px;
  font-weight: 600;
  color: var(--text);
  transition: background .35s ease, border-color .35s ease, color .35s ease, transform .35s ease, opacity .35s ease;
}
.chip.active { background: color-mix(in srgb, var(--accent) 25%, var(--panel-2)); border-color: var(--accent); color: var(--accent); }
.chip.in-window { background: color-mix(in srgb, var(--accent) 14%, var(--panel-2)); border-color: color-mix(in srgb, var(--accent) 50%, var(--border)); }
.chip.match { background: color-mix(in srgb, var(--good) 25%, var(--panel-2)); border-color: var(--good); color: var(--good); }
.chip.bad { background: color-mix(in srgb, var(--bad) 22%, var(--panel-2)); border-color: var(--bad); color: var(--bad); }
.chip.dim { opacity: .32; }
.chip.swap { transform: translateY(-6px) scale(1.06); border-color: var(--accent-2); color: var(--accent-2); }
.chip.done { background: color-mix(in srgb, var(--good) 14%, var(--panel-2)); border-color: color-mix(in srgb, var(--good) 45%, var(--border)); }

.pointer {
  position: absolute;
  top: 0;
  transform: translateX(var(--x, 0px));
  transition: transform .35s cubic-bezier(.4,0,.2,1);
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 52px;
  font-size: 10px;
  font-family: var(--mono);
  font-weight: 700;
  color: var(--accent-2);
}
.pointer .arrow { font-size: 14px; line-height: 1; }
.pointer.p-1 { color: var(--accent); }
.pointer.p-2 { color: var(--accent-2); }
.pointer.p-3 { color: var(--good); }
.pointer.p-4 { color: var(--bad); }

/* linked list */
.ll-track { display: flex; align-items: center; padding: 20px 4px; overflow-x: auto; }
.ll-node-wrap { display: flex; align-items: center; }
.ll-node {
  width: 54px;
  height: 54px;
  border-radius: 50%;
  background: var(--panel-2);
  border: 2px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-weight: 700;
  font-size: 15px;
  position: relative;
  flex-shrink: 0;
  transition: background .35s ease, border-color .35s ease, color .35s ease;
}
.ll-node.active { background: color-mix(in srgb, var(--accent) 25%, var(--panel-2)); border-color: var(--accent); color: var(--accent); }
.ll-node.match { background: color-mix(in srgb, var(--good) 22%, var(--panel-2)); border-color: var(--good); color: var(--good); }
.ll-node.dim { opacity: .35; }
.ll-node-labels {
  position: absolute;
  top: -30px;
  display: flex;
  gap: 3px;
  flex-wrap: wrap;
  justify-content: center;
  width: 90px;
  left: 50%;
  transform: translateX(-50%);
}
.ll-node-labels span {
  font-size: 9.5px;
  font-family: var(--mono);
  font-weight: 700;
  padding: 1px 5px;
  border-radius: 4px;
  background: var(--panel-2);
  border: 1px solid var(--border);
  white-space: nowrap;
}
.ll-arrow {
  width: 34px;
  height: 2px;
  background: var(--muted);
  position: relative;
  flex-shrink: 0;
  transition: background .3s ease, transform .3s ease;
}
.ll-arrow::after {
  content: '';
  position: absolute;
  right: -1px;
  top: -4px;
  border: 5px solid transparent;
  border-left-color: var(--muted);
  transition: border-color .3s ease;
}
.ll-arrow.reversed { transform: scaleX(-1); }
.ll-arrow.active-link { background: var(--accent-2); }
.ll-arrow.active-link::after { border-left-color: var(--accent-2); }
.ll-arrow.dim { opacity: .25; }
.ll-null {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  margin-left: 8px;
}

/* tree */
.tree-wrap { display: flex; gap: 26px; align-items: flex-start; }
.tree-svg-wrap { position: relative; }
.tree-node-el {
  position: absolute;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--panel-2);
  border: 2px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-weight: 700;
  font-size: 13px;
  transform: translate(-50%, -50%);
  transition: background .35s ease, border-color .35s ease, color .35s ease;
}
.tree-node-el.active { background: color-mix(in srgb, var(--accent) 28%, var(--panel-2)); border-color: var(--accent); color: var(--accent); box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent) 18%, transparent); }
.tree-node-el.visited { background: color-mix(in srgb, var(--dim) 60%, var(--panel-2)); color: var(--muted); }
.tree-node-el.queued { border-color: var(--accent-2); color: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 14%, var(--panel-2)); }
.tree-node-el.path { border-color: var(--accent-2); color: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 18%, var(--panel-2)); }
.tree-node-el.match { border-color: var(--good); color: var(--good); background: color-mix(in srgb, var(--good) 20%, var(--panel-2)); }
.tree-node-el.dim { opacity: .3; }
.tree-side {
  min-width: 150px;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 12px;
  background: var(--panel-2);
}
.tree-side h4 {
  margin: 0 0 8px;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--muted);
}
.tree-side ul { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 5px; }
.tree-side li {
  font-family: var(--mono);
  font-size: 12.5px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 4px 8px;
  transition: background .3s ease, border-color .3s ease;
}
.tree-side li.top { border-color: var(--accent); color: var(--accent); }
.tree-side .empty { color: var(--muted); font-size: 11.5px; font-style: italic; }

/* intervals */
.interval-wrap { width: 100%; }
.interval-axis {
  position: relative;
  height: 140px;
  width: 100%;
  border-bottom: 2px solid var(--border);
}
.interval-bar {
  position: absolute;
  height: 26px;
  border-radius: 7px;
  background: var(--panel-2);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 700;
  color: var(--text);
  transition: left .4s cubic-bezier(.4,0,.2,1), width .4s cubic-bezier(.4,0,.2,1), background .3s ease, border-color .3s ease, opacity .3s ease, top .3s ease;
}
.interval-bar.active { background: color-mix(in srgb, var(--accent) 25%, var(--panel-2)); border-color: var(--accent); color: var(--accent); z-index: 2; }
.interval-bar.merged { background: color-mix(in srgb, var(--good) 22%, var(--panel-2)); border-color: var(--good); color: var(--good); }
.interval-bar.dim { opacity: .35; }
.interval-tick {
  position: absolute;
  bottom: -18px;
  transform: translateX(-50%);
  font-family: var(--mono);
  font-size: 10px;
  color: var(--muted);
}

/* bits */
.bits-wrap { display: flex; flex-direction: column; gap: 10px; align-items: flex-start; }
.bits-row { display: flex; align-items: center; gap: 10px; }
.bits-row .row-label { font-family: var(--mono); font-size: 11.5px; color: var(--muted); min-width: 90px; }
.bit-group { display: flex; gap: 3px; }
.bit {
  width: 26px;
  height: 32px;
  border-radius: 5px;
  background: var(--panel-2);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 700;
  transition: background .35s ease, border-color .35s ease, color .35s ease, opacity .35s ease, transform .35s ease;
}
.bit.active { background: color-mix(in srgb, var(--accent) 25%, var(--panel-2)); border-color: var(--accent); color: var(--accent); }
.bit.match { background: color-mix(in srgb, var(--good) 22%, var(--panel-2)); border-color: var(--good); color: var(--good); }
.bit.cancelled { opacity: .2; transform: scale(.85); }
.bits-row.result .row-label { color: var(--accent-2); font-weight: 700; }
.bits-row.result .bit { border-color: var(--accent-2); }

::-webkit-scrollbar { width: 9px; height: 9px; }
::-webkit-scrollbar-thumb { background: var(--dim); border-radius: 5px; }
::-webkit-scrollbar-track { background: transparent; }

@media (max-width: 1100px) {
  body { grid-template-columns: 220px 1fr; }
  .code-panel { display: none; }
}

/* ---- directed-graph view (topological sort) ---- */
.graph-badge {
  position: absolute;
  transform: translate(-50%, 0);
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--muted);
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0 6px;
  line-height: 15px;
  white-space: nowrap;
  z-index: 2;
}

/* ---- light/dark toggle ---- */
.theme-btn {
  position: absolute;
  top: 14px;
  right: 14px;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--panel-2);
  color: var(--text);
  font-size: 15px;
  cursor: pointer;
  line-height: 1;
}
.theme-btn:hover { border-color: var(--accent); }
.sidebar { position: relative; }