/* AI 学习小站 - 主页样式(自包含,无外部依赖) */
:root {
  --bg: #0a0f1e;
  --surface: #111831;
  --surface-2: #161f3f;
  --border: rgba(148, 163, 200, 0.16);
  --text: #e7ebf7;
  --muted: #93a0bf;
  --accent: #10b981;
  --accent-2: #38bdf8;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  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;
}
.container { max-width: 980px; margin: 0 auto; padding: 0 24px; }
a { color: inherit; text-decoration: none; }

.site-header {
  position: sticky; top: 0; z-index: 10;
  background: rgba(10, 15, 30, 0.85);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}
.header-inner { display: flex; align-items: center; justify-content: space-between; height: 60px; }
.brand { font-weight: 700; display: flex; align-items: center; gap: 10px; }
.brand-mark {
  width: 30px; height: 30px; border-radius: 8px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  display: inline-flex; align-items: center; justify-content: center;
  font-size: 12px; font-weight: 800; color: #04121f;
}
.nav { display: flex; gap: 24px; font-size: 14px; color: var(--muted); }
.nav a:hover { color: var(--text); }

.hero {
  padding: 92px 0 80px;
  text-align: center;
  background:
    radial-gradient(600px 300px at 25% 0%, rgba(16, 185, 129, 0.16), transparent 60%),
    radial-gradient(600px 300px at 75% 10%, rgba(56, 189, 248, 0.14), transparent 60%);
}
.badge {
  display: inline-block; font-size: 13px; color: var(--accent-2);
  border: 1px solid rgba(56, 189, 248, 0.35); border-radius: 999px;
  padding: 4px 14px; margin-bottom: 22px;
}
.hero h1 { font-size: 44px; line-height: 1.3; font-weight: 800; }
.grad {
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.sub { color: var(--muted); max-width: 640px; margin: 18px auto 30px; font-size: 17px; }
.cta-row { display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }
.btn { padding: 12px 28px; border-radius: 10px; font-size: 15px; font-weight: 600; }
.btn-primary { background: linear-gradient(90deg, var(--accent), var(--accent-2)); color: #04121f; }
.btn-primary:hover { filter: brightness(1.1); }
.btn-ghost { border: 1px solid var(--border); }
.btn-ghost:hover { border-color: var(--muted); }

.section { padding: 68px 0; }
.section-alt { background: var(--surface); border-block: 1px solid var(--border); }
h2 { font-size: 28px; font-weight: 800; margin-bottom: 10px; }
.section-sub { color: var(--muted); margin-bottom: 30px; }

.card {
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: 12px; padding: 24px;
}
.about-card p { font-size: 15px; color: var(--text); }
.chips { list-style: none; display: flex; flex-wrap: wrap; gap: 10px; margin-top: 20px; }
.chips li {
  font-size: 13px; color: var(--muted);
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 999px; padding: 5px 14px;
}

.timeline { display: flex; flex-direction: column; gap: 0; }
.tl-item {
  display: flex; gap: 22px; padding: 22px 0;
  border-left: 2px solid var(--border);
  margin-left: 8px; padding-left: 28px; position: relative;
}
.tl-item::before {
  content: ""; position: absolute; left: -7px; top: 32px;
  width: 12px; height: 12px; border-radius: 50%;
  background: var(--surface); border: 2px solid var(--muted);
}
.tl-item.now::before { border-color: var(--accent); background: var(--accent); }
.tl-year { font-weight: 800; font-size: 16px; color: var(--accent-2); min-width: 56px; }
.tl-item h3 { font-size: 17px; margin-bottom: 6px; }
.tl-item p { font-size: 14px; color: var(--muted); }
.tl-badge {
  font-size: 11px; font-weight: 700; color: #04121f;
  background: var(--accent); border-radius: 999px; padding: 2px 10px;
  margin-left: 10px; vertical-align: 2px;
}

.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.grid-3 .card h3 { font-size: 16px; margin-bottom: 10px; color: var(--accent-2); }
.grid-3 .card p { font-size: 14px; color: var(--muted); }
.project-card { transition: border-color 0.15s, transform 0.15s; }
.project-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.project-card h3 { color: var(--text); }
.arrow { display: inline-block; margin-top: 12px; font-size: 13px; color: var(--accent); }

.footer { border-top: 1px solid var(--border); padding: 30px 0; text-align: center; font-size: 13px; color: var(--muted); }
.footer a { color: var(--accent-2); }
.footer .muted { color: #5b688a; margin-top: 4px; }

@media (max-width: 860px) {
  .nav { display: none; }
  .hero h1 { font-size: 30px; }
  .hero { padding: 56px 0 48px; }
  .grid-3 { grid-template-columns: 1fr; }
  .tl-item { flex-direction: column; gap: 4px; }
  h2 { font-size: 23px; }
}