:root {
  --fg: #1c1d21; --fg2: #555a64; --fg3: #8a8f99; --line: #e3e5e9; --bg: #f6f7f9; --card: #fff;
  --accent: #2f5fd0; --accent-bg: #edf2fd; --ok: #1f8a4c; --ok-bg: #e8f6ee; --warn: #b26a00; --warn-bg: #fdf3e2;
  --bad: #c03a3a; --bad-bg: #fbeaea; --radius: 8px;
}
* { box-sizing: border-box; }
html { scroll-padding-top: 96px; }
body { margin: 0; font: 15px/1.6 -apple-system, BlinkMacSystemFont, "PingFang SC", "Helvetica Neue", Arial, sans-serif; color: var(--fg); background: var(--bg); }
a { color: var(--accent); text-decoration: none; } a:hover { text-decoration: underline; }
header { position: sticky; top: 0; z-index: 10; background: var(--card); border-bottom: 1px solid var(--line); }
.bar { max-width: 1060px; margin: 0 auto; padding: 10px 20px 4px; display: flex; justify-content: space-between; align-items: baseline; gap: 16px; }
.brand b { font-size: 17px; margin-right: 10px; } .brand span { color: var(--fg3); font-size: 13px; }
.countdown { font-size: 13px; color: var(--fg2); white-space: nowrap; } .countdown b { color: var(--bad); font-size: 15px; }
nav { max-width: 1060px; margin: 0 auto; padding: 0 12px; display: flex; gap: 2px; overflow-x: auto; }
nav a { padding: 8px 12px 9px; color: var(--fg2); border-bottom: 2px solid transparent; white-space: nowrap; font-size: 14px; }
nav a:hover { text-decoration: none; color: var(--fg); }
nav a.active { color: var(--accent); border-bottom-color: var(--accent); font-weight: 600; }
main { max-width: 1060px; margin: 0 auto; padding: 22px 20px 80px; }
h1 { font-size: 22px; margin: 4px 0 6px; } h2 { font-size: 18px; margin: 26px 0 10px; } h3 { font-size: 16px; margin: 18px 0 8px; }
h4 { font-size: 14.5px; margin: 14px 0 6px; } h5 { font-size: 14px; margin: 10px 0 4px; }
.sub { color: var(--fg2); margin: 0 0 14px; }
.muted { color: var(--fg3); font-size: 13px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 18px; margin: 12px 0; }
.grid { display: grid; gap: 10px; } .g4 { grid-template-columns: repeat(4, minmax(0, 1fr)); } .g3 { grid-template-columns: repeat(3, minmax(0, 1fr)); } .g2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
@media (max-width: 820px) { .g4, .g3 { grid-template-columns: repeat(2, minmax(0, 1fr)); } .g2 { grid-template-columns: 1fr; } }
.fact { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 10px 12px; }
.fact .k { font-size: 12px; color: var(--fg3); } .fact .v { font-weight: 600; } .fact .n { font-size: 12.5px; color: var(--fg2); }
.note { background: var(--accent-bg); border-radius: 6px; padding: 8px 12px; margin: 8px 0; font-size: 14px; }
.warn { background: var(--warn-bg); border-radius: 6px; padding: 8px 12px; margin: 8px 0; font-size: 14px; }
.tbl { overflow-x: auto; } table { border-collapse: collapse; width: 100%; font-size: 14px; background: var(--card); }
table.csg { margin: 6px 0 14px; } table.csg td:first-child { white-space: nowrap; }
th, td { border-bottom: 1px solid var(--line); padding: 6px 10px; text-align: left; vertical-align: top; }
th { color: var(--fg2); font-weight: 600; font-size: 13px; background: #fafbfc; }
code { background: #f0f1f4; border-radius: 4px; padding: 0 4px; font-size: 0.92em; }
ul, ol { padding-left: 22px; margin: 6px 0; } li { margin: 3px 0; } p { margin: 6px 0; }
.pill { display: inline-block; font-size: 12px; padding: 1px 8px; border-radius: 999px; background: #eef0f3; color: var(--fg2); margin: 0 4px 2px 0; white-space: nowrap; }
.pill.type { background: var(--accent-bg); color: var(--accent); }
.pill.ok { background: var(--ok-bg); color: var(--ok); } .pill.retry { background: var(--warn-bg); color: var(--warn); } .pill.no { background: var(--bad-bg); color: var(--bad); }
.filters { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 4px; }
.filters button, .btn { font: inherit; font-size: 13px; border: 1px solid var(--line); background: var(--card); color: var(--fg2); border-radius: 999px; padding: 3px 11px; cursor: pointer; }
.filters button.on { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn { border-radius: 6px; padding: 4px 12px; } .btn:hover { border-color: #c7cbd2; color: var(--fg); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; } .btn.primary:hover { color: #fff; opacity: 0.92; }
.btn.okb.on { background: var(--ok); border-color: var(--ok); color: #fff; } .btn.retryb.on { background: var(--warn); border-color: var(--warn); color: #fff; } .btn.nob.on { background: var(--bad); border-color: var(--bad); color: #fff; }
.q { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); margin: 14px 0; }
.q .qh { display: flex; gap: 8px; align-items: baseline; padding: 10px 16px; border-bottom: 1px solid var(--line); flex-wrap: wrap; }
.q .qh .qid { font-weight: 700; color: var(--fg3); font-size: 13px; } .q .qh .qt { font-weight: 600; flex: 1; min-width: 200px; }
.q .qb { padding: 6px 16px 12px; }
.q .acts { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; margin-top: 8px; }
.q .acts .sp { flex: 1; }
.reveal { border-top: 1px dashed var(--line); margin-top: 10px; padding-top: 6px; }
.reveal > .lbl { font-size: 12px; color: var(--fg3); font-weight: 600; letter-spacing: 0.03em; }
.reveal.sol { background: #fbfcfe; margin-left: -16px; margin-right: -16px; padding-left: 16px; padding-right: 16px; }
.hidden { display: none !important; }
.fig { margin: 8px 0; overflow-x: auto; } .fig svg { max-width: 100%; height: auto; }
details.box { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); margin: 10px 0; }
details.box > summary { cursor: pointer; padding: 10px 16px; list-style: none; display: flex; gap: 10px; align-items: baseline; flex-wrap: wrap; }
details.box > summary::-webkit-details-marker { display: none; }
details.box > summary::before { content: "▸"; color: var(--fg3); width: 10px; } details.box[open] > summary::before { content: "▾"; }
details.box > summary .t { font-weight: 600; } details.box > .body { padding: 0 18px 12px; border-top: 1px solid var(--line); }
.sec-label { font-size: 12px; font-weight: 700; color: var(--fg3); letter-spacing: 0.04em; margin: 12px 0 2px; }
.timer { position: sticky; top: 86px; z-index: 5; background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 8px 14px; display: flex; gap: 12px; align-items: center; margin: 10px 0; }
.timer .clock { font-variant-numeric: tabular-nums; font-size: 20px; font-weight: 700; } .timer .clock.low { color: var(--bad); }
.score-in { width: 64px; font: inherit; padding: 2px 6px; border: 1px solid var(--line); border-radius: 4px; }
.bar-mini { height: 6px; background: #eceef1; border-radius: 3px; overflow: hidden; min-width: 60px; } .bar-mini > i { display: block; height: 100%; background: var(--ok); }
.cs-wrap { max-width: 100%; height: 900px; overflow: auto; -webkit-overflow-scrolling: touch; border: 1px solid var(--line); border-radius: var(--radius); background: #ddd; }
iframe.cs { display: block; width: 100%; height: 100%; border: 0; background: #ddd; }
.tylink { font-weight: 600; }
.tabs { display: flex; gap: 2px; border-bottom: 1px solid var(--line); margin: 8px 0 10px; }
.tab { font: inherit; font-size: 13.5px; border: none; background: none; padding: 6px 12px 7px; color: var(--fg2); border-bottom: 2px solid transparent; cursor: pointer; margin-bottom: -1px; }
.tab:hover { color: var(--fg); } .tab.on { color: var(--accent); border-bottom-color: var(--accent); font-weight: 600; }
.pane[data-pane="exp"] p, .pane[data-pane="exp"] li, .reveal.walk p, .reveal.walk li { line-height: 1.8; }
.pane h4, .reveal.walk h4 { margin: 20px 0 6px; padding-left: 8px; border-left: 3px solid var(--accent); font-size: 15px; }
.pane h4:first-child { margin-top: 6px; }
details.box.intro > .body p, details.box.intro > .body li { line-height: 1.8; }
.reveal.walk { background: #fffcf3; margin-left: -16px; margin-right: -16px; padding-left: 16px; padding-right: 16px; }
body.print h2.pb { break-before: page; } body.print h2 { font-size: 15pt; margin-top: 4mm; } body.print h3 { font-size: 12.5pt; }
body.print .reveal.walk { background: none; margin: 2mm 0 0; padding: 2mm 0 0; }
body.print .sec-label { margin-top: 3mm; }
.c-red { color: #d62728; font-weight: 600; } .c-blue { color: #1f6fb4; font-weight: 600; } .c-green { color: #2a9d3a; font-weight: 600; }
.c-orange { color: #ef6c00; font-weight: 600; } .c-gold { background: #ffd54f; padding: 0 3px; border-radius: 3px; }
.runs { background: #f7f9fc; border: 1px solid var(--line); border-left: 4px solid #8fb0e0; border-radius: 8px; padding: 4px 14px 2px; margin: 2px 0 14px; font-size: 14.5px; }
.runs-h { font-weight: 700; color: #2f4f86; margin: 6px 0 0; }
.runs table { font-size: 13.5px; } .runs p { margin: 6px 0; }
body.print .runs { background: none; }
.lock { max-width: 420px; margin: 48px auto; text-align: center; }
.lock form { display: flex; gap: 8px; margin-top: 16px; }
.lock input { flex: 1; min-width: 0; font-size: 16px; padding: 9px 12px; border: 1px solid var(--line); border-radius: 8px; }
.lockmsg { color: var(--fg3); min-height: 1.5em; margin-top: 10px; }
.en { color: #5c6f91; font-weight: 400; font-size: .92em; font-style: normal; }
.en-t { color: #5c6f91; font-weight: 400; font-size: 13px; }
h2 .en-t { font-size: .7em; }
.fig-help { font-size: 12.5px; margin-top: 2px; } .fig-help a { color: var(--fg3); } .fig-help a:hover { color: var(--accent); }
.trace { border: 1px solid var(--line); border-radius: var(--radius); padding: 10px 14px; margin: 12px 0; background: #fcfdff; }
.tr-title { font-weight: 600; margin-bottom: 4px; }
.tr-frame .fig { margin: 4px 0; } .tr-cap { min-height: 3.2em; font-size: 14.5px; line-height: 1.75; background: #f4f6fa; border-radius: 6px; padding: 6px 10px; }
.tr-ctl { display: flex; gap: 8px; align-items: center; margin: 8px 0 4px; flex-wrap: wrap; } .tr-pos { color: var(--fg2); font-size: 13px; min-width: 120px; text-align: center; }
details.tr-tbl > summary { cursor: pointer; color: var(--fg3); font-size: 13px; margin-top: 4px; }
body.print .fig-help, body.print .tr-ctl { display: none !important; }
body.print .trace { background: none; border: 1px solid #bbb; break-inside: auto; }
body.print .tr-frame { display: block !important; break-inside: avoid; margin-bottom: 2mm; } body.print .tr-frame .fig svg { max-height: 45mm; width: auto; }
body.print .tr-cap { background: none; padding: 0; min-height: 0; font-size: 10pt; }
/* print mode */
body.print { background: #fff; font-size: 11pt; }
body.print header { display: none; } body.print main { max-width: none; padding: 0; }
body.print .q { border: none; margin: 0 0 6mm; break-inside: auto; } body.print .q .qh { border-bottom: 1px solid #999; padding: 0 0 2mm; }
body.print .q .qb { padding: 1mm 0; } body.print .space { border: 1px dashed #bbb; border-radius: 4px; margin-top: 2mm; }
body.print .reveal.sol { background: none; margin: 2mm 0 0; padding: 2mm 0 0; }
body.print h1 { font-size: 16pt; } body.print .papermeta { font-size: 10pt; color: #444; margin-bottom: 5mm; }
@page { size: A4; margin: 14mm 15mm; }
.qlang { margin: 6px 0 10px; } .qlang > p:first-of-type { display: inline; }
.qlang .lang, .bi2 .lang { display: inline-block; font-size: 11.5px; font-weight: 700; color: #fff; background: #5c6f91; border-radius: 4px; padding: 0 6px; margin-right: 8px; vertical-align: 1px; }
.qlang.zh { border-left: 3px solid #d7deea; padding-left: 10px; color: #2d3340; } .qlang.zh .lang { background: #8d9bb6; }
.bi2 { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 18px; } .bi2 .lang { margin: 4px 0 2px; }
.meta { background: #fff7e0; border: 1px solid #f1dfab; border-radius: 6px; padding: 6px 12px; margin: 6px 0 12px; line-height: 1.75; }
.meta > b { color: #9a6b00; margin-right: 8px; } .meta p { display: inline; margin: 0; }
.en-block { color: #33415c; background: #f4f6fb; border-radius: 6px; padding: 4px 12px; margin: 8px 0; }
.reveal.solzh { background: #fbfbfd; margin-left: -16px; margin-right: -16px; padding-left: 16px; padding-right: 16px; }
.reveal.pat { background: #f6fbf6; margin-left: -16px; margin-right: -16px; padding-left: 16px; padding-right: 16px; }
.pill.src-practice { background: #e8f1ff; color: #2f5fa8; } .pill.src-mock { background: #fff0e3; color: #a85a12; } .pill.src-past { background: #e9f6ea; color: #2e7a3a; }
h2.grp { margin-top: 34px; border-bottom: 2px solid var(--line); padding-bottom: 4px; }
details.tsum { border-color: #b9cbe6; } details.tsum > summary .t { color: #2f4f86; }
body.print .acts { display: none !important; } body.print .reveal { border-top: 1px dashed #bbb; }
body.print .reveal.solzh, body.print .reveal.pat { background: none; margin: 2mm 0 0; padding: 2mm 0 0; }
body.print .meta { background: none; }
@media (max-width: 600px) {
  .bar { flex-wrap: wrap; gap: 0 12px; padding: 8px 14px 2px; } .brand span { display: none; } .countdown { font-size: 12.5px; }
  main { padding: 14px 12px 60px; } details.box > summary { padding: 9px 12px; } details.box > .body { padding: 0 10px 10px; }
  .katex-display { overflow-x: auto; overflow-y: hidden; padding: 2px 0; }
  p .katex, li .katex, td .katex, .tr-cap .katex { display: inline-block; max-width: 100%; overflow-x: auto; overflow-y: hidden; vertical-align: middle; }
  .cs-wrap { height: 70vh; } iframe.cs { width: 794px; height: 2400px; }
  .tr-ctl { gap: 6px; } .tr-ctl .btn { padding: 5px 9px; } .tr-pos { min-width: 0; flex: 1; }
}
@media (max-width: 760px) { .bi2 { grid-template-columns: minmax(0, 1fr); gap: 4px; } }

/* cheat sheet explained */
details.box.csx > summary .csx-num { background: #1c1d21; color: #fff; border-radius: 4px; padding: 0 7px; font-weight: 700; }
.csx-kind, .csx-exam { background: var(--accent-bg); border-radius: 6px; padding: 6px 12px; margin: 10px 0; line-height: 1.8; font-size: 14.5px; }
.csx-exam { background: var(--warn-bg); }
.csx-kind p, .csx-exam p { margin: 3px 0; }
.csx-head { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.3fr); gap: 16px; font-size: 12.5px; color: var(--fg3); border-bottom: 1px solid var(--line); margin: 10px 0 0; padding-bottom: 3px; }
.csx-row { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.3fr); gap: 16px; padding: 9px 0; border-bottom: 1px dashed var(--line); }
.csx-en { font-family: "Arial Narrow", Arial, sans-serif; font-size: 14.5px; line-height: 1.6; background: #f6f7f9; border-radius: 6px; padding: 7px 9px; overflow-x: auto; }
.csx-en .vi { margin: 2px 0; font-family: inherit; }
.csx-en .cap { font-size: 12.5px; color: var(--fg2); text-align: center; line-height: 1.5; }
.csx-zh { font-size: 14.5px; line-height: 1.8; min-width: 0; }
.csx-zh ul { margin: 2px 0; padding-left: 18px; } .csx-zh li { margin: 3px 0; } .csx-zh p { margin: 4px 0; }
.csx-lab { display: inline-block; min-width: 20px; text-align: center; font-weight: 700; border: 1px solid #333; border-radius: 3px; margin-right: 6px; font-size: 12px; padding: 0 3px; font-family: sans-serif; }
.csx-tbl table.x { font-size: 13.5px; } .csx-tbl table.x td, .csx-tbl table.x th { border: 1px solid var(--line); padding: 3px 6px; vertical-align: top; }
.csx-tbl table.x th { background: #eef0f3; }
.csx-toc div { margin: 6px 0; line-height: 1.9; } .csx-toc a { display: inline-block; margin: 0 10px 0 0; font-size: 13.5px; white-space: nowrap; }
@media (max-width: 900px) { .csx-head { display: none; } .csx-row { grid-template-columns: minmax(0, 1fr); gap: 6px; } }
body.print .csx-row { grid-template-columns: minmax(0, 1fr) minmax(0, 1.3fr); }
body.print details.box.csx { break-inside: auto; }
body.print .csx-head { display: grid; }