/* ==============================================================
   DSA REVISION — STYLES
   ============================================================== */
:root {
  --bg-dark: #0b0f19;
  --bg-panel: #111827;
  --bg-card: #1f293d;
  --bg-code: #0d1322;
  --border-color: #2b3648;
  --border-soft: #202a3c;
  --text-main: #f3f4f6;
  --text-muted: #9ca3af;
  --text-dim: #6b7280;
  --accent-cyan: #38bdf8;
  --accent-purple: #c084fc;
  --accent-green: #34d399;
  --accent-amber: #fbbf24;
  --accent-red: #f87171;
  --accent-blue: #60a5fa;
  --font: 'Inter', system-ui, -apple-system, sans-serif;
  --mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, monospace;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: var(--font);
  background: var(--bg-dark);
  color: var(--text-main);
  height: 100vh; overflow: hidden;
  display: flex; flex-direction: column;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Header ---------- */
header {
  height: 54px; flex: 0 0 54px;
  background: var(--bg-panel);
  border-bottom: 1px solid var(--border-color);
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 16px; gap: 16px; z-index: 30;
}
.logo-section { display: flex; align-items: center; gap: 12px; min-width: 0; }
.logo-badge {
  background: linear-gradient(135deg, var(--accent-purple), var(--accent-blue));
  color: #fff; font-weight: 700; padding: 5px 9px; border-radius: 6px;
  font-size: 11px; letter-spacing: 0.6px;
}
.title-block { display: flex; flex-direction: column; }
.app-title { font-size: 14px; font-weight: 700; }
.app-tagline { font-size: 11px; color: var(--text-muted); }
.header-search { flex: 1; max-width: 420px; }
.header-search input {
  width: 100%; height: 32px; padding: 0 12px;
  background: var(--bg-dark); border: 1px solid var(--border-color);
  border-radius: 8px; color: var(--text-main); font-family: var(--font); font-size: 13px;
}
.header-search input:focus { outline: none; border-color: var(--accent-cyan); }
.header-right .hint { font-size: 11px; color: var(--text-dim); }

/* ---------- Shell ---------- */
.shell { flex: 1; display: flex; min-height: 0; }

/* ---------- Sidebar ---------- */
.sidebar {
  width: 290px; flex: 0 0 290px;
  background: var(--bg-panel);
  border-right: 1px solid var(--border-color);
  overflow-y: auto; padding: 14px 10px 40px;
}
.side-head { font-size: 11px; text-transform: uppercase; letter-spacing: 0.8px;
  color: var(--text-dim); padding: 6px 10px 10px; font-weight: 600; }
.cat-item {
  display: flex; align-items: center; gap: 10px;
  padding: 9px 10px; border-radius: 8px; cursor: pointer;
  font-size: 13px; color: var(--text-main); margin-bottom: 2px;
  border: 1px solid transparent; transition: background .12s;
}
.cat-item:hover { background: var(--bg-card); }
.cat-item.active { background: var(--bg-card); border-color: var(--accent-cyan); }
.cat-item.empty { opacity: .42; }
.cat-icon { width: 20px; text-align: center; font-size: 14px; }
.cat-name { flex: 1; }
.cat-count { font-size: 11px; color: var(--text-dim); font-variant-numeric: tabular-nums; }

/* ---------- Main ---------- */
.main { flex: 1; overflow-y: auto; padding: 26px 30px 80px; min-width: 0; }
.page-title { font-size: 26px; font-weight: 700; margin-bottom: 6px; }
.page-sub { font-size: 13px; color: var(--text-muted); margin-bottom: 22px; max-width: 780px; line-height: 1.6; }

/* ---------- Problem cards (category view) ---------- */
.prob-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(310px, 1fr)); gap: 12px; }
.prob-card {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 10px; padding: 14px 15px; cursor: pointer;
  transition: border-color .12s, transform .12s;
}
.prob-card:hover { border-color: var(--accent-cyan); transform: translateY(-1px); }
.prob-card-top { display: flex; align-items: flex-start; justify-content: space-between; gap: 10px; margin-bottom: 8px; }
.prob-name { font-size: 14px; font-weight: 600; line-height: 1.35; }
.prob-num { font-size: 11px; color: var(--text-dim); font-variant-numeric: tabular-nums; flex-shrink: 0; }
.prob-meta { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; }
.chip {
  font-size: 10.5px; padding: 3px 7px; border-radius: 5px;
  background: #162034; color: var(--text-muted); border: 1px solid var(--border-soft);
}
.chip-easy   { color: var(--accent-green);  border-color: #14532d; background: #0d2019; }
.chip-medium { color: var(--accent-amber);  border-color: #4d3a10; background: #211a08; }
.chip-hard   { color: var(--accent-red);    border-color: #5a2020; background: #230f0f; }
.chip-new    { color: var(--accent-cyan);   border-color: #164e63; background: #082030; }
.chip-pattern{ color: var(--accent-purple); border-color: #3b2a52; background: #180f26; }

/* ---------- Problem page ---------- */
.back-link {
  display: inline-flex; align-items: center; gap: 6px; font-size: 12.5px;
  color: var(--accent-cyan); cursor: pointer; margin-bottom: 14px;
}
.back-link:hover { text-decoration: underline; }
.prob-header { margin-bottom: 18px; }
.prob-title { font-size: 25px; font-weight: 700; margin-bottom: 8px; line-height: 1.25; }

.two-col { display: grid; grid-template-columns: minmax(0,1.15fr) minmax(0,1fr); gap: 20px; align-items: start; }
@media (max-width: 1180px) { .two-col { grid-template-columns: 1fr; } }

.col-label {
  font-size: 10.5px; text-transform: uppercase; letter-spacing: 0.9px;
  color: var(--text-dim); font-weight: 700; margin-bottom: 10px;
}

/* blocks */
.block {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 10px; margin-bottom: 14px; overflow: hidden;
}
.block-head {
  display: flex; align-items: center; gap: 9px;
  padding: 11px 14px; font-size: 13px; font-weight: 600;
  border-bottom: 1px solid var(--border-soft); background: #18213400;
}
.block-head .dot { width: 7px; height: 7px; border-radius: 50%; flex-shrink: 0; }
.dot-q { background: var(--accent-cyan); }
.dot-b { background: var(--accent-red); }
.dot-o { background: var(--accent-green); }
.block-body { padding: 13px 14px; font-size: 13.2px; line-height: 1.65; color: #dde3ec; }
.block-body p + p { margin-top: 9px; }
.block-body code { font-family: var(--mono); font-size: 12px; background: #0d1322;
  padding: 1.5px 5px; border-radius: 4px; color: var(--accent-cyan); }
.block-body b { color: #fff; font-weight: 600; }

/* examples / constraints */
.example { background: var(--bg-code); border: 1px solid var(--border-soft);
  border-radius: 7px; padding: 9px 11px; margin-top: 9px; font-family: var(--mono); font-size: 11.8px; line-height: 1.7; }
.example .lbl { color: var(--text-dim); }
.example .note { color: var(--text-muted); font-family: var(--font); font-size: 12px; display: block; margin-top: 5px; }
.constraints { margin-top: 10px; font-size: 12px; color: var(--text-muted); }
.constraints li { margin-left: 16px; font-family: var(--mono); font-size: 11.5px; line-height: 1.8; }

/* code */
pre.code {
  margin: 0; padding: 13px 14px; background: var(--bg-code);
  font-family: var(--mono); font-size: 12.3px; line-height: 1.65;
  overflow-x: auto; color: #e6edf3; border-top: 1px solid var(--border-soft);
}
.tok-kw { color: #ff7b72; }
.tok-def { color: #d2a8ff; }
.tok-str { color: #a5d6ff; }
.tok-num { color: #79c0ff; }
.tok-com { color: #7d8590; font-style: italic; }
.tok-bi  { color: #ffa657; }

.cx-bar { display: flex; gap: 8px; padding: 9px 14px; border-top: 1px solid var(--border-soft); background: #131b2c; }
.cx-pill { font-family: var(--mono); font-size: 11.5px; padding: 3px 8px; border-radius: 5px;
  background: #0d1322; border: 1px solid var(--border-soft); color: var(--text-muted); }
.cx-bad { color: var(--accent-red); }
.cx-good { color: var(--accent-green); }

.why-fail { padding: 11px 14px; background: #1d1414; border-top: 1px solid #3a1f1f;
  font-size: 12.6px; line-height: 1.6; color: #f0d5d5; }
.why-fail b { color: #ffb4b4; }

/* right column sections */
.sec { border-bottom: 1px solid var(--border-soft); }
.sec:last-child { border-bottom: none; }
.sec-head {
  display: flex; align-items: center; gap: 9px; padding: 11px 14px;
  cursor: pointer; font-size: 12.8px; font-weight: 600; user-select: none;
}
.sec-head:hover { background: #1a2438; }
.sec-head .arrow { margin-left: auto; color: var(--text-dim); font-size: 10px; transition: transform .15s; }
.sec.open .sec-head .arrow { transform: rotate(90deg); }
.sec-ico { font-size: 13px; width: 17px; text-align: center; }
.sec-body { padding: 0 14px 13px; font-size: 13px; line-height: 1.68; color: #dde3ec; display: none; }
.sec.open .sec-body { display: block; }
.sec-body ul { margin-left: 17px; }
.sec-body li { margin-bottom: 6px; }
.sec-body code { font-family: var(--mono); font-size: 11.8px; background: #0d1322;
  padding: 1.5px 5px; border-radius: 4px; color: var(--accent-cyan); }
.sec-body b { color: #fff; font-weight: 600; }

.insight-box {
  background: linear-gradient(135deg, #14243a, #131c2e);
  border: 1px solid #2a3f5c; border-left: 3px solid var(--accent-cyan);
  border-radius: 8px; padding: 12px 14px; font-size: 13.5px; line-height: 1.6; color: #e8f0fa;
}
.steps { counter-reset: s; list-style: none; margin-left: 0 !important; }
.steps li { counter-increment: s; position: relative; padding-left: 27px; margin-bottom: 8px; }
.steps li::before {
  content: counter(s); position: absolute; left: 0; top: 1px;
  width: 19px; height: 19px; border-radius: 50%;
  background: var(--bg-code); border: 1px solid var(--border-color);
  color: var(--accent-cyan); font-size: 10.5px; font-weight: 700;
  display: flex; align-items: center; justify-content: center; font-family: var(--mono);
}
table.cx { width: 100%; border-collapse: collapse; font-size: 12.3px; margin-top: 4px; }
table.cx th, table.cx td { padding: 7px 9px; text-align: left; border-bottom: 1px solid var(--border-soft); }
table.cx th { color: var(--text-dim); font-weight: 600; font-size: 11px; text-transform: uppercase; letter-spacing: .5px; }
table.cx td { font-family: var(--mono); font-size: 11.8px; }
table.cx td.lbl { font-family: var(--font); color: var(--text-muted); }
.rel-row { display: flex; flex-wrap: wrap; gap: 6px; }
.rel-chip {
  font-size: 11.5px; padding: 4px 9px; border-radius: 6px; cursor: pointer;
  background: #162034; border: 1px solid var(--border-soft); color: var(--accent-cyan);
}
.rel-chip:hover { border-color: var(--accent-cyan); }
.rel-chip.ext { color: var(--text-muted); cursor: default; }
.rel-chip.ext:hover { border-color: var(--border-soft); }

.empty-state { color: var(--text-muted); font-size: 13.5px; line-height: 1.7; max-width: 620px; }
.empty-state b { color: var(--text-main); }

/* ---------- story ---------- */
.story {
  background: linear-gradient(135deg, #1a1430, #161a2e);
  border: 1px solid #342a52; border-left: 3px solid var(--accent-purple);
  border-radius: 8px; padding: 13px 15px;
  font-size: 13.6px; line-height: 1.72; color: #e9e4f5;
}
.story b { color: #fff; }

/* ---------- visual trace ---------- */
.viz {
  background: #0d1322; border: 1px solid var(--border-color);
  border-radius: 9px; padding: 15px 14px 12px; margin-top: 2px;
}
.viz-stage { display: flex; justify-content: center; padding: 4px 0 2px; overflow-x: auto; }

/* cells */
.cells { display: flex; gap: 6px; }
.cellwrap { display: flex; flex-direction: column; align-items: center; gap: 4px; }
.cell {
  min-width: 38px; height: 38px; border-radius: 7px;
  display: flex; align-items: center; justify-content: center;
  font-family: var(--mono); font-size: 13px; font-weight: 500;
  background: #182238; border: 1px solid var(--border-color); color: #cfd8e6;
  transition: background .15s, border-color .15s, transform .15s; padding: 0 7px;
}
.cell.dim    { opacity: .32; }
.cell.hitL   { background: #16304a; border-color: var(--accent-cyan);   color: #bfe8ff; }
.cell.hitR   { background: #2c1d46; border-color: var(--accent-purple); color: #e6d4ff; }
.cell.hitB   { background: #123326; border-color: var(--accent-green);  color: #b6f2d8; }
.cell.hitX   { background: #3a1a1a; border-color: var(--accent-red);    color: #ffc9c9; }
.cell.held   { background: #3a2e12; border-color: var(--accent-amber);  color: #ffe3a3; }
.cell-idx { font-size: 9.5px; color: var(--text-dim); font-family: var(--mono); }
.ptr { font-size: 10.5px; font-family: var(--mono); font-weight: 700; height: 13px; letter-spacing: .3px; }
.ptr-l { color: var(--accent-cyan); }
.ptr-r { color: var(--accent-purple); }
.ptr-h { color: var(--accent-amber); }

/* bars */
.bars { display: flex; align-items: flex-end; gap: 3px; height: 130px; }
.barwrap { display: flex; flex-direction: column; align-items: center; justify-content: flex-end;
  height: 100%; position: relative; }
.barcol { width: 26px; height: 100%; display: flex; flex-direction: column; justify-content: flex-end; }
.water { background: repeating-linear-gradient(45deg,#1d4f78,#1d4f78 4px,#22598a 4px,#22598a 8px);
  border-top: 1px solid #4aa3e0; }
.bar { background: #3b4a63; border-radius: 2px 2px 0 0; }
.bar.hitL { background: var(--accent-cyan); }
.bar.hitR { background: var(--accent-purple); }
.bar.hitB { background: var(--accent-green); }

/* nodes */
.nodes { display: flex; align-items: center; gap: 2px; flex-wrap: wrap; }
.node {
  min-width: 34px; height: 32px; border-radius: 6px; padding: 0 8px;
  display: flex; align-items: center; justify-content: center;
  background: #182238; border: 1px solid var(--border-color);
  font-family: var(--mono); font-size: 12.5px; color: #cfd8e6;
}
.node.hitL { background: #16304a; border-color: var(--accent-cyan); color: #bfe8ff; }
.node.hitR { background: #2c1d46; border-color: var(--accent-purple); color: #e6d4ff; }
.node.hitB { background: #123326; border-color: var(--accent-green); color: #b6f2d8; }
.node.hitX { background: #3a1a1a; border-color: var(--accent-red);   color: #ffc9c9; }
.node.held { background: #3a2e12; border-color: var(--accent-amber); color: #ffe3a3; }
.node.dim  { opacity: .32; }
.arrow { color: var(--text-dim); font-size: 13px; font-family: var(--mono); }
.arrow.rev { color: var(--accent-amber); }
.arrow.cut { color: var(--accent-red); font-weight: 700; }
.nodewrap { display: flex; flex-direction: column; align-items: center; gap: 3px; }

/* category groups: done vs to-do */
.group-head {
  display: flex; align-items: center; gap: 10px;
  margin: 26px 0 12px; padding-bottom: 8px;
  border-bottom: 1px solid var(--border-color);
}
.group-head:first-of-type { margin-top: 14px; }
.group-label { font-size: 13px; font-weight: 700; letter-spacing: .4px; text-transform: uppercase; }
.group-done .group-label { color: var(--accent-green); }
.group-todo .group-label { color: var(--accent-cyan); }
.group-todo { border-bottom-color: #164e63; margin-top: 34px; }
.group-count {
  font-family: var(--mono); font-size: 11.5px; padding: 1px 8px; border-radius: 10px;
  background: var(--bg-card); border: 1px solid var(--border-color); color: var(--text-dim);
}
.group-hint { font-size: 11.5px; color: var(--text-dim); margin-left: auto; }

/* home stats */
.stats { display: flex; flex-wrap: wrap; gap: 10px; margin: 18px 0 22px; }
.stat {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 10px; padding: 12px 18px; min-width: 92px;
}
.stat-n { font-size: 22px; font-weight: 700; color: var(--accent-cyan); font-family: var(--mono); }
.stat-l { font-size: 11px; color: var(--text-dim); text-transform: uppercase; letter-spacing: .5px; margin-top: 2px; }

/* grid */
.gridwrap { display: flex; flex-direction: column; gap: 4px; flex: 0 0 auto; }
.grow { display: flex; gap: 4px; }
.gcell { position: relative; min-width: 34px; width: 34px; height: 34px; font-size: 12.5px; }
.gtag {
  position: absolute; right: 1px; bottom: 0px;
  font-size: 8.5px; font-family: var(--mono); color: var(--accent-amber); line-height: 1;
}
.gptr {
  position: absolute; left: 50%; transform: translateX(-50%); top: -13px;
  font-size: 9.5px; font-family: var(--mono); font-weight: 700;
  color: var(--accent-cyan); white-space: nowrap;
}

/* tree */
.treewrap { position: relative; margin: 0 auto; flex: 0 0 auto; }
.tsvg { position: absolute; left: 0; top: 0; overflow: visible; }
.tl { stroke: var(--border-color); stroke-width: 1.5; }
.tl.on { stroke: var(--accent-green); stroke-width: 2.5; }
.tnodewrap { position: absolute; transform: translate(-50%, -50%); }
.tnode {
  min-width: 32px; width: auto; height: 32px; padding: 0 7px;
  border-radius: 16px; font-size: 12px; white-space: nowrap;
}
.tnode.dim { opacity: .3; }
.tptr {
  position: absolute; left: 50%; transform: translateX(-50%); top: -15px;
  font-size: 10px; font-family: var(--mono); font-weight: 700; white-space: nowrap;
}
.tnote {
  position: absolute; left: 50%; transform: translateX(-50%); top: 34px;
  font-size: 10px; font-family: var(--mono); color: var(--accent-amber); white-space: nowrap;
}

/* caption + controls */
.viz-cap {
  margin-top: 11px; font-size: 12.8px; line-height: 1.6; color: #d8e0ec;
  min-height: 38px; padding: 9px 11px; background: #131c2e;
  border-radius: 7px; border: 1px solid var(--border-soft);
}
.viz-cap b { color: #fff; }
.viz-cap .ok { color: var(--accent-green); font-weight: 600; }
.viz-ctl { display: flex; align-items: center; gap: 7px; margin-top: 10px; }
.viz-btn {
  background: #182238; border: 1px solid var(--border-color); color: var(--text-main);
  border-radius: 6px; padding: 4px 10px; font-size: 12px; cursor: pointer; font-family: var(--font);
}
.viz-btn:hover:not(:disabled) { border-color: var(--accent-cyan); }
.viz-btn:disabled { opacity: .3; cursor: default; }
.viz-step { font-size: 11.5px; color: var(--text-dim); font-family: var(--mono); }
.viz-play { margin-left: auto; }
.viz-legend { font-size: 10.5px; color: var(--text-dim); margin-top: 8px; font-family: var(--mono); }
.viz-legend .kl { color: var(--accent-cyan); }
.viz-legend .kr { color: var(--accent-purple); }
.viz-legend .kh { color: var(--accent-amber); }