:root {
  --c-bg: #ffffff;
  --c-bg-soft: #f7f8fa;
  --c-text: #1f2328;
  --c-text-soft: #57606a;
  --c-text-muted: #8b949e;
  --c-border: #e6e8eb;
  --c-accent: #2f5fb3;
  --c-accent-soft: #eaf1fb;
  --radius: 10px;
  --shadow: 0 1px 2px rgba(0,0,0,0.04), 0 4px 12px rgba(0,0,0,0.04);
  --max: 1100px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.7;
  color: var(--c-text);
  background: var(--c-bg);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--c-accent);
  text-decoration: none;
}
a:hover { text-decoration: underline; }

img { max-width: 100%; display: block; }

.container {
  max-width: var(--max);
  margin: 0 auto;
  padding: 0 24px;
}

/* Header */
.site-header {
  border-bottom: 1px solid var(--c-border);
  background: rgba(255,255,255,0.9);
  backdrop-filter: saturate(180%) blur(8px);
  position: sticky;
  top: 0;
  z-index: 10;
}
.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}
.brand {
  font-weight: 600;
  font-size: 17px;
  color: var(--c-text);
  letter-spacing: 0.2px;
}
.brand:hover { text-decoration: none; }
.brand small {
  color: var(--c-text-muted);
  font-weight: 400;
  margin-left: 8px;
  font-size: 13px;
}
nav.main-nav a {
  color: var(--c-text-soft);
  margin-left: 24px;
  font-size: 15px;
}
nav.main-nav a:hover,
nav.main-nav a.active {
  color: var(--c-accent);
  text-decoration: none;
}

/* Hero */
.hero {
  padding: 80px 0 60px;
  background: linear-gradient(180deg, var(--c-accent-soft) 0%, #ffffff 100%);
  border-bottom: 1px solid var(--c-border);
}
.hero h1 {
  font-size: 38px;
  line-height: 1.3;
  margin: 0 0 16px;
  font-weight: 700;
  letter-spacing: -0.5px;
}
.hero p.lead {
  font-size: 18px;
  color: var(--c-text-soft);
  max-width: 720px;
  margin: 0 0 24px;
}
.hero .meta {
  color: var(--c-text-muted);
  font-size: 14px;
}

/* Section */
section {
  padding: 64px 0;
  border-bottom: 1px solid var(--c-border);
}
section:last-of-type { border-bottom: none; }
section h2 {
  font-size: 26px;
  margin: 0 0 12px;
  font-weight: 600;
  letter-spacing: -0.3px;
}
section .section-lead {
  color: var(--c-text-soft);
  margin: 0 0 32px;
  font-size: 16px;
}

/* Cards */
.grid {
  display: grid;
  gap: 20px;
  grid-template-columns: repeat(3, 1fr);
}
.grid.two { grid-template-columns: repeat(2, 1fr); }
@media (max-width: 800px) {
  .grid, .grid.two { grid-template-columns: 1fr; }
}

.card {
  background: var(--c-bg);
  border: 1px solid var(--c-border);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
}
.card h3 {
  font-size: 17px;
  margin: 0 0 8px;
  font-weight: 600;
}
.card p {
  color: var(--c-text-soft);
  margin: 0;
  font-size: 15px;
}
.card .icon {
  width: 36px;
  height: 36px;
  border-radius: 8px;
  background: var(--c-accent-soft);
  color: var(--c-accent);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  margin-bottom: 12px;
}

/* Definition list */
.def-list {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 12px 24px;
}
.def-list dt {
  color: var(--c-text-muted);
  font-size: 15px;
}
.def-list dd {
  margin: 0;
  color: var(--c-text);
  font-size: 15px;
}
@media (max-width: 600px) {
  .def-list { grid-template-columns: 1fr; gap: 4px 0; }
  .def-list dd { margin-bottom: 12px; }
}

/* Article content */
.article {
  max-width: 760px;
  margin: 0 auto;
  padding: 48px 0;
}
.article h1 {
  font-size: 30px;
  margin: 0 0 8px;
  font-weight: 700;
}
.article .article-meta {
  color: var(--c-text-muted);
  font-size: 14px;
  margin-bottom: 32px;
}
.article h2 {
  font-size: 20px;
  margin: 32px 0 12px;
  font-weight: 600;
}
.article p, .article li {
  color: var(--c-text);
  font-size: 15px;
  line-height: 1.8;
}
.article ul, .article ol {
  padding-left: 22px;
}

/* Footer */
.site-footer {
  background: var(--c-bg-soft);
  border-top: 1px solid var(--c-border);
  padding: 40px 0 32px;
  color: var(--c-text-muted);
  font-size: 14px;
}
.site-footer .container {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  flex-wrap: wrap;
  gap: 24px;
}
.site-footer .foot-col { min-width: 220px; }
.site-footer .foot-col strong {
  color: var(--c-text-soft);
  font-weight: 600;
  display: block;
  margin-bottom: 8px;
  font-size: 14px;
}
.site-footer a { color: var(--c-text-muted); }
.site-footer a:hover { color: var(--c-accent); }
.site-footer .icp {
  margin-top: 24px;
  padding-top: 20px;
  border-top: 1px solid var(--c-border);
  width: 100%;
  text-align: center;
  font-size: 13px;
}

/* Utilities */
.text-center { text-align: center; }
.muted { color: var(--c-text-muted); }