:root {
  --bg: #f8f7f4;
  --panel: #ffffff;
  --ink: #1d2025;
  --muted: #5f6670;
  --faint: #8b929b;
  --line: #e4e1da;
  --accent: #3b5bdb;
  --accent-ink: #ffffff;
  --accent-soft: #e9eeff;
  --code-bg: #f5f4f0;
  --warn-bg: #fff6e0;
  --warn-line: #e8c46a;
  --good: #2f9e44;
  --bad: #e03131;
  --heat-0: #eceae4;
  --heat-1: #c9ead2;
  --heat-2: #8fd3a4;
  --heat-3: #4fb873;
  --heat-4: #2b8a4b;
  --cf: #1971c2; --lc: #e8590c; --cses: #2f9e44; --oa: #7048e8; --ac: #495057; --cc: #8d5524; --other: #868e96;
  --radius: 10px;
  --mono: ui-monospace, "SFMono-Regular", "JetBrains Mono", Menlo, Consolas, monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, Ubuntu, sans-serif;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #131519; --panel: #1a1d22; --ink: #e6e8ec; --muted: #a0a7b1; --faint: #7a828c; --line: #2a2f37;
    --accent: #8ea2ff; --accent-ink: #10131a; --accent-soft: #232a47; --code-bg: #15181c;
    --warn-bg: #2d2615; --warn-line: #7a6326;
    --heat-0: #24282e; --heat-1: #1d3b28; --heat-2: #24603a; --heat-3: #2f8a4f; --heat-4: #40b86a;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #131519; --panel: #1a1d22; --ink: #e6e8ec; --muted: #a0a7b1; --faint: #7a828c; --line: #2a2f37;
  --accent: #8ea2ff; --accent-ink: #10131a; --accent-soft: #232a47; --code-bg: #15181c;
  --warn-bg: #2d2615; --warn-line: #7a6326;
  --heat-0: #24282e; --heat-1: #1d3b28; --heat-2: #24603a; --heat-3: #2f8a4f; --heat-4: #40b86a;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body { background: var(--bg); color: var(--ink); font: 15px/1.6 var(--sans); }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
h1, h2, h3 { line-height: 1.25; margin: 0 0 .5em; }
h1 { font-size: 1.7rem; letter-spacing: -.01em; }
h2 { font-size: 1.12rem; margin-top: 1.8em; }
h3 { font-size: 1rem; }
code { font-family: var(--mono); font-size: .88em; background: var(--code-bg); padding: .1em .35em; border-radius: 5px; }
pre { margin: 0; }
pre code, pre code.hljs { display: block; padding: 14px 16px; overflow-x: auto; background: var(--code-bg); border-radius: var(--radius); font-size: 13px; line-height: 1.55; }
table { border-collapse: collapse; width: 100%; font-size: .93rem; }
th, td { text-align: left; padding: 7px 10px; border-bottom: 1px solid var(--line); vertical-align: top; }
th { font-weight: 600; color: var(--muted); font-size: .8rem; text-transform: uppercase; letter-spacing: .04em; }
kbd { font: 11px var(--mono); border: 1px solid var(--line); border-radius: 4px; padding: 1px 5px; color: var(--muted); }
button { font: inherit; color: inherit; }

/* ---------- top bar */
.topbar { position: sticky; top: 0; z-index: 30; display: flex; align-items: center; gap: 14px; height: 54px; padding: 0 16px; background: var(--panel); border-bottom: 1px solid var(--line); }
.brand { font-weight: 750; font-size: 1.05rem; color: var(--ink); white-space: nowrap; }
.brand:hover { text-decoration: none; }
.tabs { display: flex; gap: 2px; }
.tabs a { color: var(--muted); padding: 6px 11px; border-radius: 8px; font-weight: 550; white-space: nowrap; }
.tabs a:hover { background: var(--accent-soft); text-decoration: none; color: var(--ink); }
.tabs a.active { color: var(--accent); background: var(--accent-soft); }
.pill[hidden] { display: none; }
.pill { display: inline-block; min-width: 18px; padding: 0 6px; border-radius: 9px; background: var(--accent); color: var(--accent-ink); font-size: 11px; line-height: 18px; text-align: center; margin-left: 3px; }
.search-btn { margin-left: auto; display: flex; align-items: center; gap: 8px; background: var(--bg); border: 1px solid var(--line); border-radius: 8px; padding: 6px 10px; color: var(--muted); cursor: pointer; min-width: 190px; }
.search-btn kbd { margin-left: auto; }
.icon-btn { display: grid; place-items: center; width: 34px; height: 34px; border: 1px solid transparent; background: none; border-radius: 8px; cursor: pointer; color: var(--muted); }
.icon-btn:hover { background: var(--accent-soft); color: var(--ink); }
.menu-btn { display: none; }

/* ---------- layout */
.layout { display: grid; grid-template-columns: 290px minmax(0, 1fr); min-height: calc(100vh - 54px); }
.sidebar { position: sticky; top: 54px; height: calc(100vh - 54px); overflow-y: auto; border-right: 1px solid var(--line); background: var(--panel); padding: 12px 10px 40px; }
.main { padding: 28px 40px 80px; max-width: 980px; width: 100%; }
.scrim { display: none; }

.side-filter { width: 100%; padding: 7px 10px; border: 1px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--ink); font: inherit; font-size: .9rem; margin-bottom: 10px; }
.cat > summary { list-style: none; cursor: pointer; display: flex; align-items: center; gap: 6px; padding: 6px 8px; border-radius: 7px; font-weight: 650; font-size: .92rem; }
.cat > summary::-webkit-details-marker { display: none; }
.cat > summary::before { content: "›"; display: inline-block; width: 10px; color: var(--faint); transition: transform .15s; }
.cat[open] > summary::before { transform: rotate(90deg); }
.cat > summary:hover { background: var(--accent-soft); }
.cat .count { margin-left: auto; font-size: .75rem; color: var(--faint); font-weight: 500; }
.concept { padding: 3px 0 4px 18px; }
.concept-title { font-size: .76rem; text-transform: uppercase; letter-spacing: .05em; color: var(--faint); padding: 6px 8px 2px; }
.vlink { display: flex; align-items: center; gap: 6px; padding: 3px 8px; border-radius: 6px; color: var(--ink); font-size: .9rem; }
.vlink:hover { background: var(--accent-soft); text-decoration: none; }
.vlink.planned { color: var(--faint); }
.vlink:not(.planned) { font-weight: 560; }
.vlink.active { background: var(--accent); color: var(--accent-ink); }
.vlink .n { margin-left: auto; font-size: .72rem; padding: 0 6px; border-radius: 8px; background: var(--heat-2); color: var(--ink); }
.vlink.active .n { background: var(--accent-ink); color: var(--accent); }

/* ---------- common bits */
.crumb { color: var(--muted); font-size: .88rem; margin-bottom: 6px; }
.lead { color: var(--muted); margin-top: -.2em; }
.badge.wrap { white-space: normal; }
.badge { display: inline-flex; align-items: center; gap: 4px; font-size: .74rem; font-weight: 650; padding: 1px 8px; border-radius: 6px; border: 1px solid var(--line); color: var(--muted); white-space: nowrap; }
.plat { color: #fff; border: none; }
.plat-CF { background: var(--cf); } .plat-LC { background: var(--lc); } .plat-CSES { background: var(--cses); }
.plat-OA { background: var(--oa); } .plat-AC { background: var(--ac); } .plat-CC { background: var(--cc); } .plat-OTHER { background: var(--other); }
.chip { display: inline-block; font-size: .8rem; padding: 2px 9px; border-radius: 14px; background: var(--accent-soft); color: var(--accent); margin: 2px 4px 2px 0; }
.chip:hover { text-decoration: none; filter: brightness(.96); }
.chip.planned { background: transparent; border: 1px dashed var(--line); color: var(--faint); }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px 18px; }
.stack > * + * { margin-top: 12px; }
.note { background: var(--warn-bg); border: 1px solid var(--warn-line); border-radius: var(--radius); padding: 10px 14px; font-size: .92rem; }
.muted { color: var(--muted); }
.btn { border: 1px solid var(--line); background: var(--panel); border-radius: 8px; padding: 7px 14px; cursor: pointer; font-weight: 550; }
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn.good { border-color: var(--good); color: var(--good); }
.btn.bad { border-color: var(--bad); color: var(--bad); }
.row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.spacer { flex: 1; }
.empty { color: var(--muted); padding: 18px; border: 1px dashed var(--line); border-radius: var(--radius); text-align: center; }

/* ---------- variant page */
.signals { margin: 0; padding: 0; list-style: none; }
.signals li { position: relative; padding: 6px 10px 6px 30px; border-radius: 8px; }
.signals li::before { content: "◆"; position: absolute; left: 10px; color: var(--accent); font-size: .7rem; top: 10px; }
.signals li:nth-child(odd) { background: var(--panel); }
.idea { font-size: 1rem; }
.idea p { margin: .3em 0; }
.code-wrap { position: relative; }
.code-tools { display: flex; gap: 4px; align-items: center; margin-bottom: 6px; }
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 8px; overflow: hidden; }
.seg button { border: none; background: var(--panel); padding: 4px 12px; cursor: pointer; font-size: .85rem; color: var(--muted); }
.seg button.on { background: var(--accent-soft); color: var(--accent); font-weight: 600; }
.copy { margin-left: auto; font-size: .82rem; padding: 4px 10px; }
.pitfalls { padding-left: 1.2em; margin: 0; }
.pitfalls li { margin: 4px 0; }
.prose p { margin: .5em 0; }
.prose table { margin: .6em 0; }
.prose pre { margin: .6em 0; }
.solved-mark { color: var(--good); font-weight: 700; }
.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 40px; padding-top: 16px; border-top: 1px solid var(--line); font-size: .92rem; }

/* ---------- problem cards */
.pcard .head { display: flex; align-items: baseline; gap: 8px; flex-wrap: wrap; }
.pcard .title { font-weight: 650; font-size: 1.02rem; color: var(--ink); }
.pcard .meta { display: flex; gap: 6px; align-items: center; flex-wrap: wrap; color: var(--muted); font-size: .85rem; margin-top: 4px; }
.pcard .insight { margin-top: 10px; padding-left: 12px; border-left: 3px solid var(--accent); }
.pcard .mistakes { margin-top: 8px; padding-left: 12px; border-left: 3px solid var(--bad); color: var(--muted); font-size: .92rem; }
.pcard details { margin-top: 10px; }
.pcard summary { cursor: pointer; color: var(--muted); font-size: .88rem; }
.star { color: #f59f00; }

/* ---------- home */
.stats { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 12px; margin: 18px 0 8px; }
.stat { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 12px 14px; }
.stat b { display: block; font-size: 1.6rem; line-height: 1.2; }
.stat span { color: var(--muted); font-size: .85rem; }
a.stat:hover { text-decoration: none; border-color: var(--accent); }
.cat-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(210px, 1fr)); gap: 12px; }
.cat-card { color: var(--ink); }
.cat-card:hover { text-decoration: none; border-color: var(--accent); }
.bar { height: 6px; border-radius: 3px; background: var(--heat-0); overflow: hidden; margin: 8px 0 4px; }
.bar i { display: block; height: 100%; background: var(--accent); }
.list-row { display: flex; gap: 10px; align-items: baseline; padding: 8px 0; border-bottom: 1px solid var(--line); }
.list-row:last-child { border-bottom: none; }
.list-row .t { font-weight: 550; }

/* ---------- map */
.legend { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; font-size: .82rem; color: var(--muted); margin-bottom: 14px; }
.legend i { display: inline-block; width: 14px; height: 14px; border-radius: 4px; vertical-align: -2px; margin-right: 4px; }
.mm-cat { margin-bottom: 26px; }
.mm-cat > h2 { margin: 0 0 8px; display: flex; gap: 10px; align-items: baseline; }
.mm-cat > h2 small { color: var(--faint); font-weight: 500; font-size: .8rem; }
.mm-concepts { list-style: none; margin: 0; padding: 0 0 0 16px; border-left: 2px solid var(--line); }
.mm-concepts > li { position: relative; padding: 6px 0 6px 18px; }
.mm-concepts > li::before { content: ""; position: absolute; left: -2px; top: 19px; width: 14px; border-top: 2px solid var(--line); }
.mm-concept { font-weight: 600; font-size: .9rem; margin-bottom: 4px; }
.mm-variants { display: flex; flex-wrap: wrap; gap: 6px; }
.mm-v { display: inline-flex; gap: 6px; align-items: center; padding: 4px 10px; border-radius: 8px; font-size: .84rem; color: var(--ink); background: var(--heat-0); border: 1px solid transparent; }
.mm-v:hover { text-decoration: none; border-color: var(--accent); }
.mm-v.planned { background: transparent; border: 1px dashed var(--line); color: var(--faint); }
.mm-v.h1 { background: var(--heat-1); } .mm-v.h2 { background: var(--heat-2); } .mm-v.h3 { background: var(--heat-3); color: #fff; } .mm-v.h4 { background: var(--heat-4); color: #fff; }
.mm-v b { font-size: .75rem; }

/* ---------- log */
.filters { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 14px 0 18px; }
.filters input, .filters select { font: inherit; font-size: .9rem; padding: 6px 9px; border: 1px solid var(--line); border-radius: 8px; background: var(--panel); color: var(--ink); }
.filters input[type=search] { flex: 1; min-width: 180px; }
.filters input[type=number] { width: 118px; }
.filters label { display: flex; gap: 5px; align-items: center; font-size: .9rem; color: var(--muted); }
.day { margin: 22px 0 6px; color: var(--muted); font-size: .85rem; font-weight: 600; text-transform: uppercase; letter-spacing: .04em; }
.tabs-inline { display: flex; gap: 6px; margin-top: 10px; }

/* ---------- revise */
.flash { max-width: 720px; }
.flash .front { text-align: center; padding: 30px 20px; }
.flash .front .title { font-size: 1.4rem; font-weight: 700; }
.flash .prompt { color: var(--muted); margin: 14px 0 18px; }
.grade { display: flex; gap: 10px; justify-content: center; margin-top: 16px; }
.progress { color: var(--muted); font-size: .88rem; margin-bottom: 10px; }

/* ---------- search */
.search-overlay { position: fixed; inset: 0; z-index: 60; background: rgba(10, 12, 16, .45); display: flex; justify-content: center; padding: 10vh 16px 16px; }
.search-overlay[hidden] { display: none; }
.search-box { width: 100%; max-width: 640px; background: var(--panel); border: 1px solid var(--line); border-radius: 14px; overflow: hidden; display: flex; flex-direction: column; max-height: 75vh; box-shadow: 0 20px 60px rgba(0, 0, 0, .25); }
.search-box input { border: none; border-bottom: 1px solid var(--line); padding: 14px 16px; font: inherit; font-size: 1rem; background: var(--panel); color: var(--ink); outline: none; }
.search-results { overflow-y: auto; padding: 6px; }
.sr-group { font-size: .72rem; text-transform: uppercase; letter-spacing: .05em; color: var(--faint); padding: 8px 10px 4px; }
.sr { display: block; padding: 8px 10px; border-radius: 8px; color: var(--ink); }
.sr small { display: block; color: var(--muted); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.sr.sel, .sr:hover { background: var(--accent-soft); text-decoration: none; }

/* ---------- small screens */
@media (max-width: 900px) {
  .layout { grid-template-columns: minmax(0, 1fr); }
  .menu-btn { display: grid; }
  .sidebar { position: fixed; z-index: 50; top: 0; left: 0; bottom: 0; height: 100vh; width: min(310px, 86vw); transform: translateX(-102%); transition: transform .2s ease; }
  body.side-open .sidebar { transform: none; }
  body.side-open .scrim { display: block; position: fixed; inset: 0; z-index: 40; background: rgba(0, 0, 0, .35); }
  .main { padding: 20px 16px 70px; }
  .stats { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .search-btn { min-width: 0; }
  .search-btn .search-label, .search-btn kbd { display: none; }
  .topbar { gap: 8px; padding: 0 10px; }
}
@media (max-width: 560px) {
  .brand { display: none; }
  .tabs a { padding: 6px 8px; }
  th:nth-child(4), td:nth-child(4) { display: none; }
}