:root {
  --bg: #f7f8fa;
  --surface: #ffffff;
  --text: #1a1d23;
  --muted: #5c6570;
  --border: #e2e6eb;
  --accent: #2563eb;
  --accent-soft: #eff6ff;
  --tip-bg: #ecfdf5;
  --tip-border: #10b981;
  --warn-bg: #fff7ed;
  --warn-border: #f59e0b;
  --code-bg: #0f172a;
  --code-text: #e2e8f0;
  --toc-w: 220px;
  --max: 760px;
  --radius: 10px;
  --shadow: 0 1px 2px rgba(16, 24, 40, 0.04), 0 4px 12px rgba(16, 24, 40, 0.04);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0f14;
    --surface: #141a22;
    --text: #e8edf4;
    --muted: #9aa6b2;
    --border: #243041;
    --accent: #60a5fa;
    --accent-soft: #152238;
    --tip-bg: #0f241c;
    --tip-border: #34d399;
    --warn-bg: #2a1f0e;
    --warn-border: #fbbf24;
    --code-bg: #020617;
    --code-text: #e2e8f0;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px rgba(0, 0, 0, 0.25);
  }
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
}
a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { opacity: 0.9; }

.site-header {
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}
.site-header .inner {
  max-width: 960px;
  margin: 0 auto;
  padding: 16px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}
.brand {
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  letter-spacing: -0.02em;
}
.brand span { color: var(--muted); font-weight: 500; font-size: 0.9rem; margin-left: 8px; }
.nav a { margin-left: 14px; color: var(--muted); text-decoration: none; font-size: 0.92rem; }
.nav a:hover { color: var(--accent); }

.layout {
  max-width: calc(var(--max) + var(--toc-w) + 48px);
  margin: 0 auto;
  padding: 32px 20px 64px;
  display: grid;
  grid-template-columns: 1fr;
  gap: 28px;
}
@media (min-width: 980px) {
  .layout {
    grid-template-columns: var(--toc-w) minmax(0, var(--max));
    align-items: start;
  }
}
.layout.no-toc { max-width: var(--max); grid-template-columns: 1fr; }

.toc {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: var(--shadow);
}
@media (min-width: 980px) {
  .toc {
    position: sticky;
    top: 20px;
    max-height: calc(100vh - 40px);
    overflow: auto;
  }
}
.toc h2 {
  margin: 0 0 10px;
  font-size: 0.85rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--muted);
  font-weight: 700;
}
.toc ol { margin: 0; padding-left: 1.2rem; font-size: 0.9rem; }
.toc li { margin: 0.35rem 0; }
.toc a { color: var(--text); text-decoration: none; }
.toc a:hover { color: var(--accent); }

main.card, .card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 28px 24px 36px;
  box-shadow: var(--shadow);
  max-width: var(--max);
}
@media (min-width: 640px) {
  main.card, .card { padding: 40px 40px 48px; }
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 10px;
  flex-wrap: wrap;
}
.badge {
  background: var(--accent-soft);
  color: var(--accent);
  border-radius: 999px;
  padding: 2px 10px;
  font-weight: 600;
  font-size: 0.78rem;
}
h1 {
  margin: 0 0 12px;
  font-size: clamp(1.55rem, 3vw, 2rem);
  line-height: 1.25;
  letter-spacing: -0.02em;
}
.lead { color: var(--muted); font-size: 1.05rem; margin: 0 0 24px; }
h2 {
  margin: 2.2rem 0 0.85rem;
  font-size: 1.35rem;
  padding-top: 0.4rem;
  border-top: 1px solid var(--border);
  scroll-margin-top: 24px;
}
h2:first-of-type { border-top: none; padding-top: 0; }
h3 { margin: 1.6rem 0 0.6rem; font-size: 1.1rem; scroll-margin-top: 24px; }
p { margin: 0.75rem 0; }
ul, ol { margin: 0.6rem 0 1rem; padding-left: 1.35rem; }
li { margin: 0.35rem 0; }
blockquote {
  margin: 1rem 0;
  padding: 12px 16px;
  border-left: 4px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--text);
}
.callout {
  border-radius: var(--radius);
  border-left: 4px solid;
  padding: 12px 14px;
  margin: 1rem 0;
  background: var(--tip-bg);
  border-color: var(--tip-border);
}
.callout.warn { background: var(--warn-bg); border-color: var(--warn-border); }
.callout .label { font-weight: 700; font-size: 0.86rem; margin-bottom: 4px; }

.meta-row { color: var(--muted); font-size: 0.92rem; margin: 0 0 1.2rem; }
.tweet-list { list-style: none; padding: 0; margin: 1rem 0; }
.tweet-list li {
  margin: 0 0 12px;
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg);
}
.tweet-list .n {
  font-size: 0.78rem;
  color: var(--muted);
  font-weight: 600;
  margin-bottom: 4px;
}
.site-footer {
  max-width: 960px;
  margin: 0 auto;
  padding: 24px 20px 48px;
  color: var(--muted);
  font-size: 0.88rem;
  border-top: 1px solid var(--border);
}
.article-list { list-style: none; padding: 0; margin: 0; }
.article-list li {
  margin: 0 0 14px;
  padding: 16px 18px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow);
}
.article-list a.title {
  font-weight: 650;
  font-size: 1.05rem;
  color: var(--text);
  text-decoration: none;
}
.article-list a.title:hover { color: var(--accent); }
.article-list .date { color: var(--muted); font-size: 0.86rem; margin-top: 4px; }
.article-list .sum { color: var(--muted); font-size: 0.92rem; margin-top: 6px; }
.back { display: inline-block; margin-bottom: 16px; font-size: 0.9rem; }
.src-links { font-size: 0.9rem; }