:root {
  --bg: #ffffff;
  --bg-soft: #fafafa;
  --text: #1a1a1a;
  --text-secondary: #555555;
  --text-tertiary: #888888;
  --accent: #1a3a5c;
  --accent-soft: rgba(26, 58, 92, 0.08);
  --line: #e5e5e5;
  --line-light: #f0f0f0;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  margin: 0;
  color: var(--text);
  background: var(--bg);
  font: 17px/1.8 "PingFang SC", "Microsoft YaHei", "Noto Sans SC", sans-serif;
  letter-spacing: 0.01em;
}

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

a:hover {
  text-decoration: underline;
}

/* ---------- Navigation ---------- */
.site-nav {
  border-bottom: 1px solid var(--line);
  background: var(--bg);
}

.nav-inner {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.nav-brand {
  font: 600 18px/1.2 Georgia, "Songti SC", serif;
  color: var(--text);
  letter-spacing: -0.01em;
}

.nav-brand:hover {
  text-decoration: none;
}

.nav-links {
  display: flex;
  gap: 28px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-links a {
  font-size: 15px;
  color: var(--text-secondary);
  transition: color 0.2s;
}

.nav-links a:hover {
  color: var(--text);
  text-decoration: none;
}

.nav-links a.active {
  color: var(--text);
  font-weight: 500;
}

/* ---------- Layout ---------- */
.page-wrap {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ---------- Hero ---------- */
.hero {
  padding: 80px 0 60px;
  border-bottom: 1px solid var(--line);
}

.hero-title {
  font: 700 40px/1.15 Georgia, "Songti SC", serif;
  margin: 0 0 16px;
  letter-spacing: -0.02em;
}

.hero-subtitle {
  font: 400 20px/1.6 "PingFang SC", "Microsoft YaHei", sans-serif;
  color: var(--text-secondary);
  margin: 0 0 28px;
  max-width: 560px;
}

.hero-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.hero-tags li {
  font-size: 13px;
  color: var(--text-tertiary);
  padding: 4px 12px;
  border: 1px solid var(--line);
  border-radius: 999px;
}

/* ---------- Sections ---------- */
section {
  padding: 48px 0;
  border-bottom: 1px solid var(--line);
}

section:last-of-type {
  border-bottom: none;
}

.section-header {
  margin-bottom: 28px;
}

.section-kicker {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 0 0 8px;
}

.section-title {
  font: 700 26px/1.3 Georgia, "Songti SC", serif;
  margin: 0;
}

.section-lead {
  color: var(--text-secondary);
  margin: 12px 0 0;
  max-width: 580px;
}

/* ---------- Content blocks ---------- */
.content-block + .content-block {
  margin-top: 36px;
}

.content-block h3 {
  font: 700 20px/1.35 Georgia, "Songti SC", serif;
  margin: 0 0 12px;
}

.content-block p {
  margin: 0 0 12px;
  color: var(--text-secondary);
}

.content-block p:last-child {
  margin-bottom: 0;
}

.content-block ul {
  margin: 0;
  padding-left: 22px;
  color: var(--text-secondary);
}

.content-block li + li {
  margin-top: 8px;
}

/* ---------- Grid ---------- */
.two-col {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 32px;
}

/* ---------- Statement / Notice ---------- */
.statement {
  padding: 28px;
  background: var(--bg-soft);
  border: 1px solid var(--line-light);
  border-radius: 8px;
}

.statement p {
  color: var(--text-secondary);
  margin: 0;
  font-size: 15px;
  line-height: 1.75;
}

/* ---------- Footer ---------- */
.site-footer {
  padding: 48px 0 24px;
  border-top: 1px solid var(--line);
}

.footer-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-bottom: 32px;
}

.footer-col p:first-child {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 0 0 8px;
}

.footer-col p:last-child {
  margin: 0;
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* ---------- Beian ---------- */
.beian-bar {
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px 0 48px;
  font-size: 13px;
  color: var(--text-tertiary);
}

.beian-bar a {
  color: var(--text-tertiary);
}

.beian-bar a:hover {
  color: var(--text-secondary);
}

/* ---------- Timeline (changelog) ---------- */
.timeline {
  position: relative;
  padding-left: 24px;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 5px;
  top: 8px;
  bottom: 8px;
  width: 1px;
  background: var(--line);
}

.timeline-item {
  position: relative;
  padding-bottom: 32px;
}

.timeline-item:last-child {
  padding-bottom: 0;
}

.timeline-item::before {
  content: "";
  position: absolute;
  left: -20px;
  top: 8px;
  width: 9px;
  height: 9px;
  border-radius: 50%;
  background: var(--bg);
  border: 2px solid var(--line);
}

.timeline-item.current::before {
  border-color: var(--accent);
  background: var(--accent);
}

.timeline-date {
  font-size: 13px;
  color: var(--text-tertiary);
  margin: 0 0 4px;
}

.timeline-title {
  font: 700 17px/1.4 Georgia, "Songti SC", serif;
  margin: 0 0 6px;
}

.timeline-desc {
  color: var(--text-secondary);
  margin: 0;
  font-size: 15px;
  line-height: 1.7;
}

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  .nav-inner {
    height: 56px;
  }

  .nav-links {
    gap: 18px;
  }

  .hero {
    padding: 48px 0 40px;
  }

  .hero-title {
    font-size: 32px;
  }

  .hero-subtitle {
    font-size: 17px;
  }

  section {
    padding: 36px 0;
  }

  .two-col {
    grid-template-columns: 1fr;
    gap: 24px;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 20px;
  }

  .statement {
    padding: 20px;
  }
}