:root {
  --bg: #fbfaf7;
  --panel: #ffffff;
  --ink: #1d1d1b;
  --muted: #6b6a64;
  --line: #dddbd3;
  --soft: #f1efe8;
  --accent: #b5481f;
  --accent-soft: #f6e2d8;
  --cool: #23608f;
  --cool-soft: #dcebf5;
  --ok: #2f7a3a;
  --bad: #b3261e;
  --cell: 26px;
  --mono: ui-monospace, "Cascadia Mono", "SFMono-Regular", Menlo, Consolas, monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #161614;
    --panel: #1e1e1c;
    --ink: #e8e6df;
    --muted: #9b998f;
    --line: #36352f;
    --soft: #262622;
    --accent: #e57a4e;
    --accent-soft: #4a2a1d;
    --cool: #7db3dc;
    --cool-soft: #1d3446;
    --ok: #74c17f;
    --bad: #ef7a72;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.55 var(--sans);
}

a { color: var(--cool); }
code, kbd, .mono { font-family: var(--mono); font-size: 0.92em; }
kbd {
  border: 1px solid var(--line);
  border-bottom-width: 2px;
  border-radius: 4px;
  padding: 0 4px;
  background: var(--panel);
}

.site {
  display: flex;
  align-items: baseline;
  gap: 24px;
  max-width: 1080px;
  margin: 0 auto;
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
}
.site .home { font-weight: 650; color: var(--ink); text-decoration: none; }
.site nav { display: flex; gap: 16px; }
.site nav a { color: var(--muted); text-decoration: none; }
.site nav a[aria-current] { color: var(--ink); border-bottom: 2px solid var(--accent); }

main { max-width: 1080px; margin: 0 auto; padding: 8px 16px 64px; }
h1 { font-size: 1.9rem; margin: 28px 0 4px; letter-spacing: -0.01em; }
h2 { font-size: 1.3rem; margin: 40px 0 8px; }
h3 { font-size: 1.05rem; margin: 24px 0 6px; }
.lede { color: var(--muted); margin: 0 0 20px; max-width: 70ch; }
p, li { max-width: 75ch; }

/* ---------- simulator ---------- */

.sim {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 16px;
}

.sim-top {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 180px;
  gap: 12px;
  align-items: end;
}
label.field { display: flex; flex-direction: column; gap: 4px; font-size: 0.85rem; color: var(--muted); }
select, input, textarea, button {
  font: inherit;
  color: var(--ink);
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 6px;
}
select, input { padding: 6px 8px; min-width: 0; }
input.mono { font-family: var(--mono); }
textarea {
  width: 100%;
  min-height: 64px;
  max-height: 220px;
  padding: 8px;
  font: 14px/1.45 var(--mono);
  resize: vertical;
  word-break: break-all;
}
.code-meta { display: flex; justify-content: space-between; gap: 12px; font-size: 0.8rem; color: var(--muted); margin-top: 2px; }
.code-meta .warn { color: var(--bad); }

.controls {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin: 12px 0;
}
button {
  padding: 6px 12px;
  background: var(--soft);
  cursor: pointer;
}
button:hover:not(:disabled) { border-color: var(--muted); }
button:disabled { opacity: 0.45; cursor: default; }
button.primary { background: var(--accent); border-color: var(--accent); color: #fff; min-width: 72px; }
.controls .gap { flex: 1; }
.controls label { display: flex; align-items: center; gap: 6px; font-size: 0.85rem; color: var(--muted); }
.controls input[type="range"] { width: 120px; padding: 0; }
.controls input[type="number"] { width: 120px; }
.speed-value { font-family: var(--mono); font-size: 0.8rem; min-width: 70px; }

.status {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 20px;
  font-size: 0.9rem;
  padding: 8px 10px;
  background: var(--soft);
  border-radius: 6px;
}
.status b { font-family: var(--mono); font-weight: 600; }
.status .halted { color: var(--ok); }
.status .stopped { color: var(--bad); }

/* tapes */
.tapes { margin: 14px 0 4px; display: flex; flex-direction: column; gap: 10px; }
.tape-label { font-size: 0.8rem; color: var(--muted); display: flex; justify-content: space-between; gap: 8px; }
.tape {
  display: flex;
  overflow: hidden;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  font: 14px/1 var(--mono);
  user-select: none;
}
.cell {
  flex: 0 0 var(--cell);
  height: 34px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-right: 1px solid var(--line);
  position: relative;
}
.cell .ix { position: absolute; bottom: 1px; font-size: 8px; color: var(--muted); }
.cell.blank { color: var(--muted); opacity: 0.55; }
.cell.out { background: var(--cool-soft); font-weight: 700; }
.cell.pair-start { border-left: 2px solid var(--line); }
.cell.head { background: var(--accent); color: #fff; opacity: 1; font-weight: 700; }
.cell.partner { box-shadow: inset 0 0 0 2px var(--cool); }
.cell.rec-alt { background: var(--soft); }
.cell.rec-cur { background: var(--cool-soft); }
.cell.head .ix { color: #fff; }

.output-line { font-size: 0.95rem; margin-top: 10px; }
.output-line .mono { font-size: 1rem; }
.kind { color: var(--muted); }
.output-line .ok { color: var(--ok); }
.output-line .bad { color: var(--bad); }

/* LUTM-6 panels */
.panels { display: grid; grid-template-columns: minmax(0, 1fr); gap: 16px; margin-top: 18px; }
.panel { min-width: 0; }
.panel summary { cursor: pointer; font-weight: 600; font-size: 0.95rem; margin-bottom: 6px; }
.panel h3 { margin: 0 0 6px; font-size: 0.95rem; }
.panel .hint { font-size: 0.8rem; color: var(--muted); margin: 0 0 6px; }
.records {
  position: relative;
  max-height: 240px;
  overflow: auto;
  border: 1px solid var(--line);
  border-radius: 6px;
  font: 12.5px/1.5 var(--mono);
}
.records div { padding: 1px 8px; white-space: nowrap; display: flex; gap: 10px; }
.records div:nth-child(odd) { background: var(--soft); }
.records .cur { background: var(--cool-soft) !important; }
.records .n { color: var(--muted); flex: 0 0 64px; }
.records .txt { flex: 0 0 200px; overflow: hidden; text-overflow: ellipsis; }

.delta { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 8px; }
.delta table { border-collapse: collapse; font: 11px/1.25 var(--mono); width: 100%; table-layout: fixed; }
.delta th:first-child { width: 28px; }
.delta caption { text-align: left; font-weight: 600; font-size: 12px; padding-bottom: 2px; }
.delta caption span { font-weight: 400; color: var(--muted); font-family: var(--sans); }
.delta th { color: var(--muted); font-weight: 400; padding: 1px 2px; }
.delta td { border: 1px solid var(--line); padding: 2px; text-align: center; white-space: nowrap; }
.delta td.cur { background: var(--accent); color: #fff; }
.delta td.halt { color: var(--muted); }
.delta-legend { font-size: 0.8rem; color: var(--muted); margin-top: 6px; }

/* ---------- documentation ---------- */

.doc table { border-collapse: collapse; margin: 8px 0 16px; font-size: 0.92rem; }
.doc th, .doc td { border-bottom: 1px solid var(--line); padding: 5px 12px 5px 0; text-align: left; vertical-align: top; }
.doc th { color: var(--muted); font-weight: 500; }
.doc pre {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 10px 12px;
  overflow-x: auto;
  font: 13px/1.5 var(--mono);
}

/* ---------- landing ---------- */

.pair { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-top: 20px; }
.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 18px 20px;
  display: flex;
  flex-direction: column;
}
.card h2 { margin: 0; }
.card .sub { color: var(--muted); margin: 2px 0 12px; }
.card dl { display: grid; grid-template-columns: 110px 1fr; gap: 6px 12px; margin: 0 0 16px; font-size: 0.92rem; }
.card dt { color: var(--muted); }
.card dd { margin: 0; }
.card .open { margin-top: auto; align-self: flex-start; background: var(--accent); color: #fff; padding: 8px 16px; border-radius: 6px; text-decoration: none; }
.mini { display: flex; font: 13px/1 var(--mono); margin: 4px 0; }
.mini span { width: 22px; height: 26px; display: flex; align-items: center; justify-content: center; border: 1px solid var(--line); margin-right: -1px; }
.mini span.b { color: var(--muted); }
.mini span.gap { margin-left: 6px; }

.compare { border-collapse: collapse; width: 100%; font-size: 0.92rem; margin-top: 8px; }
.compare th, .compare td { border-bottom: 1px solid var(--line); padding: 6px 10px 6px 0; text-align: left; vertical-align: top; }
.compare th { color: var(--muted); font-weight: 500; }
.compare a { text-decoration: none; }
.compare .kind { color: var(--muted); font-size: 0.82rem; }
.compare .steps { color: var(--muted); font-family: var(--mono); font-size: 0.82rem; }
.compare .none { color: var(--muted); }

@media (max-width: 760px) {
  .sim-top, .pair, .panels { grid-template-columns: 1fr; }
  .delta { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .card dl { grid-template-columns: 1fr; gap: 0 0; }
  .card dt { margin-top: 6px; }
  .records .txt { flex-basis: 110px; }
  .sim { padding: 12px; }
}