/* 统一样式：浅/深色、卡片化网格、胶囊导航 */
:root {
  --bg:#f7f8fa; --fg:#1f2937; --muted:#6b7280; --brand:#2563eb;
  --card:#ffffff; --border:#e5e7eb; --shadow:0 6px 16px rgba(31,41,55,0.08);
  --radius:14px;
}
@media (prefers-color-scheme: dark) {
  :root { --bg:#0b0f14; --fg:#e5e7eb; --muted:#9aa0a6; --brand:#60a5fa; --card:#111827; --border:#1f2937; --shadow:0 6px 18px rgba(0,0,0,0.35); }
}
html,body { margin:0; padding:0; background:var(--bg); color:var(--fg); font-family:system-ui,-apple-system,Segoe UI,Roboto,Arial,"Noto Sans SC","Microsoft YaHei",sans-serif; }
body { font-size:16px; line-height:1.65; text-rendering:optimizeLegibility; }
header { padding:40px 24px 20px; background:linear-gradient(180deg, rgba(37,99,235,0.08), rgba(37,99,235,0.00)); border-bottom:1px solid var(--border); }
.title { font-size:28px; margin:0 0 10px; letter-spacing:0.5px; }
.sub { color:var(--muted); margin:0; font-size:14px; max-width:1000px; }

nav { position:sticky; top:0; z-index:10; display:flex; flex-wrap:wrap; gap:10px; padding:12px 24px; backdrop-filter:saturate(140%) blur(6px); background:rgba(247,248,250,0.8); border-bottom:1px solid var(--border); }
@media (prefers-color-scheme: dark) { nav { background:rgba(11,15,20,0.7); } }
nav a { padding:8px 12px; border-radius:999px; background:var(--card); color:var(--brand); border:1px solid var(--border); text-decoration:none; font-size:14px; white-space:nowrap; transition:all .18s ease; }
nav a:hover { box-shadow:var(--shadow); transform:translateY(-1px); }

main { padding:24px; max-width:1100px; margin:0 auto; display:grid; grid-template-columns:repeat(auto-fit, minmax(320px, 1fr)); gap:18px; }
section { padding:16px 18px; background:var(--card); border:1px solid var(--border); border-radius:var(--radius); box-shadow:var(--shadow); }
section h2 { margin:0 0 12px; font-size:18px; display:flex; align-items:center; gap:8px; }
section h2::before { content:"✦"; color:var(--brand); font-size:18px; }
.item { margin:10px 0; padding:6px 0; border-bottom:1px dashed var(--border); }
.item:last-child { border-bottom:0; }
.desc { color:var(--muted); font-size:13px; margin:8px 0 0; }
.katex-display { margin:8px 0; }

footer { padding:24px; color:var(--muted); font-size:12px; border-top:1px solid var(--border); max-width:1100px; margin:0 auto; }
@media print {
  nav, header { position:static; backdrop-filter:none; }
  section { box-shadow:none; border-color:#ccc; }
  body { background:#fff; color:#000; }
}

/* 入口页卡片链接 */
.grid-links { display:grid; grid-template-columns:repeat(auto-fit, minmax(240px, 1fr)); gap:16px; padding:24px; max-width:1100px; margin:0 auto; }
.card-link { display:block; padding:16px; background:var(--card); border:1px solid var(--border); border-radius:var(--radius); box-shadow:var(--shadow); color:var(--fg); text-decoration:none; }
.card-link h3 { margin:0 0 8px; font-size:17px; color:var(--brand); }
.card-link p { margin:0; color:var(--muted); font-size:13px; }