:root {
  --bg: #ffffff;
  --title: #2b2f33;
  --body: #1c1d1f;
  --blue: #1f3a8a;
  --green: #1e6b3a;
  --red: #9b1c1c;
  --line: #2b2f33;
  --soft: #eef1f7;
  --muted: #5b6168;
}
* { box-sizing: border-box; }
html, body { margin: 0; background: var(--bg); color: var(--body); font-family: "Roboto", "Helvetica Neue", Arial, sans-serif; }
h1, h2, h3 { font-family: "Montserrat", "Helvetica Neue", Arial, sans-serif; font-weight: 800; color: var(--title); margin: 0; }
code, .mono { font-family: "Courier Prime", "Courier New", monospace; }

.page { max-width: 1280px; margin: 0 auto; padding: 20px 16px 40px; }
.top { display: flex; align-items: baseline; justify-content: space-between; flex-wrap: wrap; gap: 8px; margin-bottom: 12px; }
.top h1 { font-size: 26px; }
.top .sub { color: var(--muted); font-size: 14px; }

.modes { display: flex; gap: 8px; margin-bottom: 12px; }
.modes button { font: 700 13px "Montserrat", Arial, sans-serif; padding: 8px 16px; border: 1.5px solid var(--line); background: #fff; color: var(--title); border-radius: 6px; cursor: pointer; }
.modes button.on { background: var(--blue); border-color: var(--blue); color: #fff; }

.stage { width: 100%; aspect-ratio: 16 / 9; min-height: 560px; border: 1.5px solid var(--line); border-radius: 10px; overflow: auto; padding: 24px 32px; background: #fff; }
@media (max-width: 800px) { .stage { aspect-ratio: auto; padding: 16px; } }
.stage h2 { font-size: 24px; margin-bottom: 4px; }
.tagline { color: var(--muted); margin: 0 0 14px; }

.tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 16px; }
.tabs button { font: 700 12px "Montserrat", Arial, sans-serif; padding: 6px 12px; border: 1.5px solid var(--line); background: #fff; color: var(--title); border-radius: 999px; cursor: pointer; }
.tabs button.on { background: var(--blue); color: #fff; border-color: var(--blue); }

.cols { display: grid; grid-template-columns: 1.55fr 1fr; gap: 24px; }
@media (max-width: 900px) { .cols { grid-template-columns: 1fr; } }

.analogy { display: flex; gap: 14px; align-items: center; border: 1.5px solid var(--green); border-radius: 8px; padding: 10px 14px; margin-bottom: 14px; }
.analogy svg { flex: 0 0 64px; width: 64px; height: 64px; }
.analogy .lab { font: 800 11px "Montserrat", Arial, sans-serif; color: var(--green); text-transform: uppercase; letter-spacing: .06em; }
.analogy p { margin: 2px 0 0; font-size: 14px; }

.viz { min-height: 170px; border: 1.5px dashed #b6bcc6; border-radius: 8px; padding: 14px; display: flex; align-items: center; justify-content: center; }
.viz.col { flex-direction: column-reverse; justify-content: flex-start; gap: 4px; }
.row { display: flex; flex-wrap: wrap; gap: 6px; align-items: flex-end; justify-content: center; }
.cell { position: relative; min-width: 54px; height: 54px; border: 1.5px solid var(--line); border-radius: 4px; display: flex; flex-direction: column; align-items: center; justify-content: center; font: 700 16px "Courier Prime", monospace; background: #fff; animation: pop .25s ease-out; }
.cell small { font: 700 10px "Roboto", Arial, sans-serif; color: var(--muted); }
.cell .idx { position: absolute; bottom: -18px; font: 700 10px "Roboto", Arial, sans-serif; color: var(--muted); }
.cell.hl { background: var(--blue); color: #fff; border-color: var(--blue); }
.cell.hl small { color: #cfd8f5; }
.cell.dup { border-color: var(--red); color: var(--red); }
.cell.circle { border-radius: 50%; width: 54px; }
.cell.wide { width: 150px; justify-content: center; }
.tag { font: 800 10px "Montserrat", Arial, sans-serif; text-transform: uppercase; letter-spacing: .05em; color: var(--blue); margin: 0 4px; align-self: center; }
.tag.g { color: var(--green); } .tag.r { color: var(--red); }
.ends { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; justify-content: center; }
.empty { color: var(--muted); font-style: italic; }
@keyframes pop { from { transform: scale(.6); opacity: 0; } to { transform: scale(1); opacity: 1; } }

.controls { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 14px 0 6px; }
.controls input { font: 700 14px "Courier Prime", monospace; width: 90px; padding: 7px 8px; border: 1.5px solid var(--line); border-radius: 4px; }
.controls label { font: 700 11px "Roboto", Arial, sans-serif; color: var(--muted); display: flex; flex-direction: column; gap: 2px; }
.ops { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 8px; }
.ops button, .btn { font: 700 13px "Courier Prime", monospace; padding: 8px 12px; border: 1.5px solid var(--blue); color: var(--blue); background: #fff; border-radius: 5px; cursor: pointer; }
.ops button:hover, .btn:hover { background: var(--blue); color: #fff; }
.btn.plain { border-color: var(--line); color: var(--title); }
.out { min-height: 44px; border-left: 4px solid var(--blue); background: var(--soft); padding: 8px 12px; font-size: 14px; border-radius: 0 6px 6px 0; }
.out.bad { border-color: var(--red); }
.out b { font-family: "Courier Prime", monospace; }

.facts { width: 100%; border-collapse: collapse; font-size: 13px; }
.facts th, .facts td { text-align: left; padding: 6px 8px; border-bottom: 1px solid #d9dde4; vertical-align: top; }
.facts th { font: 800 11px "Montserrat", Arial, sans-serif; color: var(--title); text-transform: uppercase; letter-spacing: .04em; }
.facts td:first-child { font-family: "Courier Prime", monospace; font-weight: 700; color: var(--blue); white-space: nowrap; }
.box { border: 1.5px solid var(--line); border-radius: 8px; padding: 10px 14px; margin-bottom: 12px; }
.box h3 { font-size: 13px; margin-bottom: 6px; }
.box ul { margin: 0; padding-left: 18px; font-size: 13px; line-height: 1.5; }

.h2h-head { display: flex; gap: 10px; align-items: end; flex-wrap: wrap; margin-bottom: 12px; }
.h2h-head input { font: 700 14px "Courier Prime", monospace; width: 220px; padding: 7px 8px; border: 1.5px solid var(--line); border-radius: 4px; }
.h2h { display: grid; grid-template-columns: 150px 1fr 190px; gap: 0; border-top: 1px solid #d9dde4; }
.h2h > div { padding: 8px 6px; border-bottom: 1px solid #d9dde4; display: flex; align-items: center; min-height: 74px; }
.h2h .hd { min-height: 0; font: 800 11px "Montserrat", Arial, sans-serif; text-transform: uppercase; color: var(--muted); letter-spacing: .05em; }
.h2h .nm { font: 800 14px "Montserrat", Arial, sans-serif; color: var(--title); flex-direction: column; align-items: flex-start; gap: 2px; }
.h2h .nm span { font: 400 11px "Roboto", Arial, sans-serif; color: var(--muted); }
.h2h .cell { min-width: 40px; height: 40px; font-size: 13px; }
.h2h .cell.wide { width: 90px; }
.h2h .rule { flex-direction: column; align-items: flex-start; font-size: 12px; gap: 2px; }
.h2h .rule b { font: 700 13px "Courier Prime", monospace; color: var(--blue); }
.legend { font-size: 12px; color: var(--muted); margin-top: 10px; }

.q-card { max-width: 820px; }
.q-scn { font: 700 20px "Montserrat", Arial, sans-serif; color: var(--title); margin: 8px 0 16px; line-height: 1.35; }
.q-opts { display: flex; flex-wrap: wrap; gap: 8px; }
.q-opts button { font: 700 13px "Montserrat", Arial, sans-serif; padding: 9px 14px; border: 1.5px solid var(--line); background: #fff; color: var(--title); border-radius: 6px; cursor: pointer; }
.q-opts button.ok { background: var(--green); color: #fff; border-color: var(--green); }
.q-opts button.no { background: var(--red); color: #fff; border-color: var(--red); }
.q-why { margin-top: 14px; font-size: 14px; min-height: 40px; }
.q-bar { font: 700 12px "Montserrat", Arial, sans-serif; color: var(--muted); }

/* ---- implementations, compare, cheat sheet ---- */
.stage { aspect-ratio: auto; min-height: 640px; }
.lab2 { font: 800 11px "Montserrat", Arial, sans-serif; color: var(--green); text-transform: uppercase; letter-spacing: .06em; }
.chips { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; margin-bottom: 10px; }
.chiplab { font: 800 11px "Montserrat", Arial, sans-serif; color: var(--muted); text-transform: uppercase; letter-spacing: .05em; margin-right: 4px; }
.chips button { font: 700 12px "Roboto", Arial, sans-serif; padding: 6px 12px; border: 1.5px solid var(--green); color: var(--green); background: #fff; border-radius: 6px; cursor: pointer; }
.chips button.on { background: var(--green); color: #fff; }
.how { font-size: 13px; line-height: 1.5; margin: 0; }
.cost { margin-top: 4px; font-size: 13px; color: var(--blue); }
.viz { flex-direction: column; gap: 10px; overflow-x: auto; min-height: 190px; }
.slot { display: flex; flex-direction: column; align-items: center; gap: 2px; }
.slot .lab, .node .lab { font: 800 9px "Montserrat", Arial, sans-serif; text-transform: uppercase; color: var(--green); height: 12px; white-space: nowrap; }
.node { display: flex; flex-direction: column; align-items: center; gap: 2px; }
.cell.empty-slot { border-style: dashed; border-color: #b6bcc6; animation: none; }
.row.arr { flex-wrap: nowrap; gap: 4px; padding-bottom: 20px; align-items: flex-start; }
.row.linked { flex-wrap: wrap; align-items: flex-end; gap: 4px; padding-bottom: 6px; }
.arrow { font: 700 14px "Courier Prime", monospace; color: var(--blue); align-self: flex-end; padding-bottom: 14px; }
.meta { font-size: 11px; color: var(--muted); text-align: center; }
.buckets { display: flex; flex-direction: column; gap: 3px; }
.bkt { display: flex; align-items: center; gap: 3px; }
.bkt .cell { min-width: 40px; height: 32px; font-size: 13px; }
.bkt .cell small { font-size: 9px; }
.cell.bidx { background: var(--soft); color: var(--muted); }
.svgwrap { max-width: 100%; overflow-x: auto; }
svg line { stroke: #2b2f33; stroke-width: 1.5; }
.tn circle { fill: #fff; stroke: #2b2f33; stroke-width: 1.5; }
.tn text { font: 700 13px "Courier Prime", monospace; fill: #1c1d1f; }
.tn text.sm { font-size: 11px; }
.tn text.tv { font: 700 10px "Roboto", Arial, sans-serif; fill: #5b6168; }
.tn.hl circle { fill: var(--blue); stroke: var(--blue); }
.tn.hl text:not(.tv) { fill: #fff; }

.panels { display: grid; gap: 14px; margin-top: 12px; }
.panel { border: 1.5px solid var(--line); border-radius: 8px; padding: 12px; min-width: 0; }
.panel h3 { font-size: 14px; margin-bottom: 8px; }
.viz2 { min-height: 150px; display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 8px; overflow-x: auto; border: 1.5px dashed #b6bcc6; border-radius: 6px; padding: 10px 6px; }
.viz2 .cell { min-width: 44px; height: 44px; font-size: 14px; }
.stat { display: flex; justify-content: space-between; margin-top: 8px; font-size: 13px; }
.stat b { font-family: "Courier Prime", monospace; font-size: 15px; }
.stat b.good { color: var(--green); }
.totbar { height: 6px; background: var(--soft); border-radius: 3px; margin: 4px 0 8px; }
.totbar i { display: block; height: 100%; background: var(--blue); border-radius: 3px; }
.pmsg { font-size: 12px; min-height: 52px; color: var(--body); }
.pmsg.bad { color: var(--red); }
.bars { display: flex; align-items: flex-end; gap: 2px; height: 46px; margin-top: 6px; border-bottom: 1px solid #b6bcc6; }
.bar { width: 10px; background: var(--blue); border-radius: 2px 2px 0 0; }
.bar.err { background: var(--red); }
.barcap { font-size: 10px; color: var(--muted); margin-top: 2px; }

.facts.big { margin-top: 8px; }
.facts.big td { font-family: "Roboto", Arial, sans-serif; font-weight: 400; color: var(--body); white-space: normal; border-bottom: 1px solid #d9dde4; }
.facts.big td.adtc, .facts.big td.opsc { font-family: "Courier Prime", monospace; }
.facts.big td.adtc b { font: 800 14px "Montserrat", Arial, sans-serif; color: var(--title); }
.facts.big td.opsc { font-size: 12px; color: var(--blue); font-weight: 700; }
.facts.big tr.first td { border-top: 2px solid var(--line); }
.facts td b { color: var(--title); }
.facts.big .mono { color: var(--blue); font-weight: 700; }
.box.note { border-color: var(--blue); background: #f6f8fd; }

/* ---- quiz review list ---- */
.q-review-list { margin-top: 16px; display: flex; flex-direction: column; gap: 12px; }
.q-review-list h3 { font-size: 16px; margin-bottom: 4px; }
.q-review-item { border: 1.5px solid var(--line); border-radius: 8px; padding: 12px 14px; background: #fff; }
.q-review-item.ok { border-color: var(--green); border-left-width: 6px; }
.q-review-item.err { border-color: var(--red); border-left-width: 6px; }
.q-review-head { display: flex; justify-content: space-between; align-items: center; margin-bottom: 6px; }
.q-review-num { font: 800 12px "Montserrat", Arial, sans-serif; text-transform: uppercase; color: var(--muted); }
.q-review-status { font: 700 12px "Roboto", Arial, sans-serif; }
.q-review-status.ok { color: var(--green); }
.q-review-status.err { color: var(--red); }
.q-review-q { font: 700 15px "Montserrat", Arial, sans-serif; color: var(--title); margin-bottom: 6px; }
.q-review-ans { font-size: 14px; margin-bottom: 4px; color: var(--title); }
.q-review-ans b { color: var(--blue); }
.q-review-why { font-size: 13px; color: var(--muted); line-height: 1.4; }