:root {
    --bg:#f4f4f2; --ink:#111; --sub:#666; --line:#d8d8d4; --card:#fff; --accent:#111;
    --code:#111; --codeink:#f2f2f0; --teach:#fff6d6; --teachline:#e2c565; --ok:#1f7a4d;
  }
  @media (prefers-color-scheme: dark) {
    :root { --bg:#0e0e0e; --ink:#f2f2f0; --sub:#9a9a96; --line:#2a2a28; --card:#181817; --accent:#f2f2f0;
      --code:#000; --codeink:#e8e8e4; --teach:#2b2610; --teachline:#6b5a1e; --ok:#5fcf95; }
  }
  * { box-sizing:border-box; margin:0; }
  html { scroll-behavior:smooth; scroll-padding-top:76px; }
  body { font-family:-apple-system,"Hiragino Sans","Noto Sans JP",sans-serif; background:var(--bg); color:var(--ink); line-height:1.8; }
  a { color:inherit; }
  code { font-family:ui-monospace,Menlo,monospace; background:var(--line); padding:1px 6px; border-radius:5px; font-size:.9em; }

  .top { position:sticky; top:0; z-index:10; background:var(--bg); border-bottom:1px solid var(--line);
    display:flex; align-items:center; gap:16px; padding:12px 28px; }
  .top .logo { font-weight:800; letter-spacing:.3em; font-size:13px; }
  .top .crumb { color:var(--sub); font-size:13px; flex:1; }
  .top a.back { text-decoration:none; font-size:13px; border:1px solid var(--line); border-radius:99px; padding:6px 14px; }
  .mode { display:flex; border:1px solid var(--line); border-radius:99px; overflow:hidden; }
  .mode button { background:none; border:0; color:var(--sub); font:inherit; font-size:13px; padding:6px 14px; cursor:pointer; }
  .mode button.on { background:var(--accent); color:var(--bg); }

  .wrap { display:grid; grid-template-columns:240px 1fr; gap:48px; max-width:1180px; margin:0 auto; padding:36px 28px 80px; }
  nav.toc { position:sticky; top:84px; align-self:start; font-size:14px; max-height:calc(100vh - 110px); overflow:auto; }
  nav.toc h4 { font-size:11px; letter-spacing:.2em; color:var(--sub); margin:16px 0 6px; }
  nav.toc a { display:block; padding:5px 10px; border-left:2px solid var(--line); text-decoration:none; color:var(--sub); }
  nav.toc a:hover { color:var(--ink); border-color:var(--accent); }

  main { min-width:0; }
  .hero .eyebrow { font-size:12px; letter-spacing:.25em; color:var(--sub); }
  .hero h1 { font-size:clamp(28px,4vw,42px); line-height:1.35; margin:8px 0 14px; }
  .lead { color:var(--sub); max-width:46em; }
  .important { margin-top:24px; border:2px solid var(--accent); border-radius:14px; padding:18px 22px; font-size:17px; font-weight:700; }
  .important small { display:block; font-size:11px; letter-spacing:.2em; color:var(--sub); font-weight:400; }

  section.block { margin-top:56px; }
  section.block > h2 { font-size:24px; padding-bottom:10px; border-bottom:1px solid var(--line); margin-bottom:20px; }
  h3 { font-size:17px; margin:26px 0 8px; }
  p { margin:8px 0; }

  table { width:100%; border-collapse:collapse; background:var(--card); border:1px solid var(--line); border-radius:12px; overflow:hidden; font-size:14px; }
  th,td { padding:10px 14px; text-align:left; border-bottom:1px solid var(--line); }
  th { font-size:12px; color:var(--sub); letter-spacing:.1em; }
  tr:last-child td { border-bottom:0; }
  td a { text-decoration:none; font-weight:700; }
  td a:hover { text-decoration:underline; }

  .ex { background:var(--card); border:1px solid var(--line); border-radius:16px; padding:26px 28px; margin-top:28px; }
  .ex header { display:flex; flex-wrap:wrap; align-items:baseline; gap:6px 14px; margin-bottom:6px; }
  .ex .no { font-size:12px; letter-spacing:.2em; color:var(--sub); }
  .ex h3 { margin:0; font-size:21px; }
  .chips { display:flex; gap:8px; margin:8px 0 14px; flex-wrap:wrap; }
  .chip { font-size:12px; border:1px solid var(--line); border-radius:99px; padding:2px 12px; }
  .goal { color:var(--sub); }
  ol.steps { list-style:none; padding:0; counter-reset:s; margin-top:18px; }
  ol.steps > li { counter-increment:s; position:relative; padding:0 0 18px 44px; }
  ol.steps > li::before { content:counter(s); position:absolute; left:0; top:0; width:28px; height:28px; border-radius:50%;
    background:var(--accent); color:var(--bg); font-weight:700; font-size:13px; display:grid; place-items:center; }
  ol.steps > li > b { display:block; }

  .prompt { position:relative; background:var(--code); color:var(--codeink); border-radius:10px; padding:14px 90px 14px 16px; margin:10px 0;
    font-family:ui-monospace,Menlo,monospace; font-size:13.5px; white-space:pre-wrap; line-height:1.7; }
  .prompt .tag { position:absolute; left:16px; top:-9px; background:var(--bg); color:var(--sub); font-family:inherit; font-size:10px; letter-spacing:.15em; padding:0 6px; border-radius:4px; }
  .prompt button { position:absolute; right:10px; top:10px; background:none; color:var(--codeink); border:1px solid #555; border-radius:6px; font:inherit; font-size:12px; padding:3px 10px; cursor:pointer; }
  .prompt button:hover { border-color:#aaa; }

  .box { border-radius:12px; padding:14px 18px; margin-top:16px; font-size:14.5px; }
  .box h4 { font-size:12px; letter-spacing:.2em; margin-bottom:6px; color:var(--sub); }
  .box ul { padding-left:1.2em; }
  .box.done { border:1px solid var(--line); }
  .box.done li { list-style:none; margin-left:-1.2em; }
  .box.done label { cursor:pointer; display:flex; gap:10px; align-items:flex-start; }
  .box.done input { margin-top:7px; accent-color:var(--ok); }
  .box.done label:has(input:checked) span { color:var(--sub); text-decoration:line-through; }
  .box.hint { background:var(--bg); border:1px dashed var(--line); }
  .box.teach { display:none; background:var(--teach); border:1px solid var(--teachline); }
  body.teacher .box.teach { display:block; }
  .box.teach h4 { color:inherit; }
  .progress { font-size:12px; color:var(--sub); margin-left:auto; }

  .diagram { background:var(--card); border:1px solid var(--line); border-radius:14px; padding:22px; font-size:14.5px; }
  .tree { display:grid; gap:10px; }
  .tree > div { border:1px solid var(--line); border-radius:10px; padding:12px 16px; }
  .tree > div:nth-child(2) { margin-left:28px; }
  .tree > div:nth-child(3) { margin-left:56px; }
  .tree > div:nth-child(4) { margin-left:84px; }
  .tree b { display:block; }
  .tree span { color:var(--sub); font-size:13px; }
  .flow { display:flex; align-items:stretch; gap:10px; flex-wrap:wrap; }
  .flow > div { flex:1; min-width:150px; border:1px solid var(--line); border-radius:12px; padding:14px; background:var(--card); }
  .flow > div b { display:block; font-size:18px; }
  .flow > div span { color:var(--sub); font-size:13px; }
  .flow > i { align-self:center; font-style:normal; font-size:22px; color:var(--sub); }

  footer { text-align:center; color:var(--sub); font-size:12px; padding:30px; border-top:1px solid var(--line); }

  @media (max-width:900px) {
    .wrap { grid-template-columns:1fr; padding:24px 16px 60px; }
    nav.toc { display:none; }
    .top { padding:10px 16px; flex-wrap:wrap; }
    .top .crumb { display:none; }
    .ex { padding:20px 18px; }
    .tree > div { margin-left:0 !important; }
  }
  @media print {
    .top, nav.toc, .prompt button { display:none; }
    .wrap { display:block; padding:0; }
    .ex { break-inside:avoid; }
  }

  .tabs { display:flex; gap:6px; }
  .tabs a { font-size:13px; text-decoration:none; color:var(--sub); border:1px solid var(--line); border-radius:99px; padding:6px 14px; }
  .tabs a.on { background:var(--accent); color:var(--bg); border-color:var(--accent); }
  .cols { display:grid; grid-template-columns:repeat(auto-fit,minmax(260px,1fr)); gap:16px; margin-top:12px; }
  .col { background:var(--card); border:1px solid var(--line); border-radius:14px; padding:18px 20px; }
  .col h4 { font-size:12px; letter-spacing:.2em; color:var(--sub); margin-bottom:8px; }
  .col ol, .col ul { padding-left:1.3em; }
  kbd { font-family:ui-monospace,Menlo,monospace; font-size:.85em; background:var(--card); border:1px solid var(--line); border-bottom-width:2px; border-radius:6px; padding:1px 7px; white-space:nowrap; }
  .note { border-left:3px solid var(--accent); background:var(--card); padding:12px 16px; margin:14px 0; border-radius:0 10px 10px 0; font-size:14.5px; }
  .gap { display:inline-block; font-size:11px; border:1px dashed var(--teachline); background:var(--teach); border-radius:6px; padding:0 8px; margin-left:8px; vertical-align:middle; font-weight:400; }
  .path { font-family:ui-monospace,Menlo,monospace; background:var(--code); color:var(--codeink); border-radius:10px; padding:12px 16px; margin:8px 0; font-size:13.5px; overflow-x:auto; }
  .path em { font-style:normal; color:#f5c451; }
  @media (max-width:900px) { .tabs { width:100%; order:5; } }