:root{
  --bg:#080e18; --card:#131f2e; --text:#e2e8f0; --muted:#94a3b8; --border:#2d3f55;
  --blue:#3b82f6; --orange:#fb923c; --callout-bg:#0f2040; --callout-fg:#93c5fd;
  --side-w:260px;
}
*{box-sizing:border-box}
html{overflow-x:hidden}
body{margin:0;background:var(--bg);color:var(--text);font-family:system-ui,-apple-system,"Segoe UI","Microsoft JhengHei",sans-serif;line-height:1.7}
a{color:#60a5fa;text-decoration:none}
a:hover{text-decoration:underline}
code{background:#07111e;color:#7dd3fc;border:1px solid rgba(59,130,246,.3);border-radius:4px;padding:0 4px;font-size:.85em}

.topbar{display:none}
.layout{display:flex;min-height:100vh}

/* 側欄目錄 */
.side{width:var(--side-w);flex:none;position:sticky;top:0;height:100vh;overflow-y:auto;background:var(--card);border-right:1px solid var(--border);padding:20px 14px}
.side .brand{display:block;font-size:1.35rem;font-weight:700;color:var(--text);margin-bottom:14px}
.side .brand span{display:block;font-size:.8rem;color:var(--muted);font-weight:400}
.side .brand.active{color:var(--orange)}
.side h3{font-size:.85rem;color:var(--orange);margin:18px 0 6px;letter-spacing:.05em}
.side h3 em{font-style:normal;color:var(--muted);font-weight:400}
.side ul{list-style:none;margin:0;padding:0}
.side li a{display:block;padding:5px 10px;border-radius:6px;color:var(--text);font-size:.92rem}
.side li a span{display:block;font-size:.72rem;color:var(--muted)}
.side li a:hover{background:#1b2b40;text-decoration:none}
.side li a.active{background:var(--callout-bg);border-left:3px solid var(--blue);color:var(--callout-fg)}
.side details summary{cursor:pointer;padding:3px 10px;font-size:.85rem;color:var(--muted)}
.side li.sub a{padding-left:24px}

/* 主內容 */
main{flex:1;min-width:0;padding:28px 40px 40px;max-width:1100px}
.crumb{font-size:.85rem;color:var(--muted);margin-bottom:6px}
h1{margin:0 0 20px;font-size:1.8rem}
h1 small{display:block;font-size:1rem;color:var(--muted);font-weight:400}
h2{margin:32px 0 12px;font-size:1.2rem;border-left:4px solid var(--orange);padding-left:10px}
h2 em{font-style:normal;color:var(--muted);font-weight:400;font-size:.9rem}
.muted{color:var(--muted)}
.callout{background:var(--callout-bg);border:1px solid rgba(59,130,246,.3);color:var(--callout-fg);border-radius:8px;padding:12px 16px;margin:20px 0}

/* 公式圖：原圖為白底，放白色卡片內避免深色背景刺眼 */
figure{margin:0 0 22px;background:#fff;border:1px solid var(--border);border-radius:10px;padding:14px;display:inline-block;max-width:100%}
figure img{display:block;max-width:100%;height:auto}
main > figure{display:table}

/* 卡片格 */
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:12px}
.card{display:block;background:var(--card);border:1px solid var(--border);border-radius:10px;padding:14px 16px;color:var(--text);position:relative}
.card:hover{border-color:var(--blue);text-decoration:none}
.card b{display:block;font-size:1.05rem}
.card span{font-size:.82rem;color:var(--muted)}
.card i{position:absolute;top:12px;right:14px;font-style:normal;font-size:.75rem;color:var(--orange)}

/* 上一頁／下一頁 */
.pager{display:flex;justify-content:space-between;gap:12px;margin-top:28px;padding-top:16px;border-top:1px solid var(--border)}
.pager a{background:var(--card);border:1px solid var(--border);border-radius:8px;padding:8px 14px}
.pager a:hover{border-color:var(--blue);text-decoration:none}

/* LaTeX 改寫頁：公式（KaTeX）＋ SVG 示意圖 */
.eqrow{display:flex;flex-wrap:wrap;align-items:center;gap:8px 28px;background:var(--card);border:1px solid var(--border);border-radius:10px;padding:14px 18px;margin:0 0 16px}
.eqrow .diagram{flex:0 1 380px;width:100%;max-width:420px;height:auto}
.eqrow .eqs{flex:1 1 300px;min-width:0}
.eqs{overflow-x:auto;overflow-y:hidden;scrollbar-color:var(--border) transparent}
.eqs.wide{background:#07111e;border:1px solid rgba(59,130,246,.3);border-radius:10px;padding:4px 18px;margin:0 0 16px}
.katex{font-size:1.15em;color:var(--text)}
.katex-display{margin:.7em 0}
.katex-display>.katex{color:#7dd3fc}
.notes{margin:8px 0 20px;padding-left:1.3em}
.notes li{margin:4px 0}
.concepts{background:var(--card);border:1px solid var(--border);border-radius:10px;padding:14px 18px 14px 2.6em;margin:0 0 20px}
.concepts li{margin:10px 0}
.diagram .lb{font-family:KaTeX_Math,"Times New Roman",serif;font-style:italic;font-size:19px;fill:var(--text)}
.diagram .lb.up{font-family:KaTeX_Main,"Times New Roman",serif;font-style:normal}
.diagram .lb.bd{font-weight:700}
.diagram line,.diagram path,.diagram ellipse{fill:none;stroke-linecap:round}
.diagram .ov{stroke:var(--text);stroke-width:1.3}
.diagram .ln-w{stroke:#e2e8f0;stroke-width:2.2}
.diagram .ln-r{stroke:#f87171;stroke-width:2.6}
.diagram .ln-v{stroke:#60a5fa;stroke-width:2.6}
.diagram .ln-v.thick{stroke-width:3.4}
.diagram .ln-o{stroke:#c084fc;stroke-width:2.4}
.diagram .ln-d{stroke:var(--muted);stroke-width:2;stroke-dasharray:3 4}
.diagram .ln-a,.diagram .ln-t{stroke:var(--text);stroke-width:1.3}
.diagram .ln-m{stroke:var(--muted);stroke-width:1.3}
.diagram .ln-u{stroke:#e2e8f0;stroke-width:3}
.diagram .ln-O{stroke:var(--orange);stroke-width:2.6}
.diagram .ln-O.thin{stroke-width:1.6}
.diagram .fill-w{fill:#e2e8f0}.diagram .fill-r{fill:#f87171}.diagram .fill-v{fill:#60a5fa}
.diagram .fill-m{fill:var(--muted)}.diagram .fill-o{fill:var(--orange)}.diagram .fill-t{fill:var(--text)}
.diagram .ln-body{fill:none;stroke:var(--muted);stroke-width:1.6}
.diagram .ln-body.solid{fill:#1b2b40}
.diagram .dot{fill:var(--text);stroke:none}
.diagram .pin{fill:var(--card);stroke:var(--text);stroke-width:1.6}
.diagram .sub{font-size:12px}
.diagram .ln-body.link{fill:var(--card);fill-opacity:.55}
.diagram .ln-body.link.top{stroke:var(--text)}
.diagram .pin-ring{fill:none;stroke:var(--text);stroke-width:1.2;stroke-dasharray:2 2}
.eqrow .diagram.small{flex:0 1 200px;max-width:220px}
.eqrow .diagram.wide{flex:1 1 100%;max-width:720px}
.diagram .lb.muted{fill:var(--muted)}
.diagram .lb.eqv{font-size:30px;fill:var(--muted)}
.diagram .use-src{fill:inherit;stroke:inherit;stroke-width:inherit}
.diagram .ln-blob{fill:rgba(45,212,191,.14);stroke:#2dd4bf;stroke-width:1.6}
.diagram .ln-rd{stroke:#f87171;stroke-width:2.2;stroke-dasharray:7 5}
.diagram .ln-r.thin{stroke-width:1.6}
.diagram .cap{font-size:14px;fill:var(--text);text-anchor:middle}
.diagram .cap.en{font-size:12px;fill:var(--muted)}
.sub-h{font-size:1rem;color:var(--callout-fg);margin:22px 0 10px}
.sub-h .katex{color:var(--callout-fg)}

/* 例題頁：題目文字＋裁切後的教科書插圖 */
.exrow{display:flex;flex-wrap:wrap;gap:16px 28px;align-items:flex-start;margin-bottom:8px}
.exrow .prob{flex:1 1 340px;min-width:0}
.exrow .prob h2{margin-top:0}
.exrow .prob p{margin:0 0 10px}
figure.crop{flex:1 1 300px;display:block;width:100%;margin:0 0 16px}
figure.crop svg{display:block;width:100%;height:auto}
details.answer{background:var(--card);border:1px solid var(--border);border-radius:10px;padding:10px 16px;margin:0 0 20px}
details.answer summary{cursor:pointer;color:var(--orange);font-weight:700}
details.answer .eqs.wide{margin-top:12px}

details.orig{margin:24px 0 8px}
details.orig summary{cursor:pointer;color:var(--muted)}
details.orig figure{display:table;margin:12px 0}

footer{margin-top:40px;padding-top:14px;border-top:1px solid var(--border);font-size:.8rem;color:var(--muted)}

/* 手機：側欄改抽屜 */
@media (max-width:860px){
  .topbar{display:flex;align-items:center;gap:12px;position:sticky;top:0;z-index:20;background:var(--card);border-bottom:1px solid var(--border);padding:10px 16px}
  .topbar a{color:var(--text);font-weight:700}
  .topbar button{background:none;border:1px solid var(--border);color:var(--text);border-radius:6px;font-size:1.1rem;padding:2px 10px;cursor:pointer}
  .side{position:fixed;top:0;left:0;z-index:30;transform:translateX(-100%);transition:transform .2s;box-shadow:4px 0 20px rgba(0,0,0,.5)}
  body.nav-open .side{transform:none}
  main{padding:18px 16px 32px}
  figure{padding:8px}
}