:root {
  --bg: #0a0f1a;
  --bg-soft: #0e1626;
  --panel: #101b30;
  --panel-border: #1d2c47;
  --text: #d7e2f2;
  --text-dim: #8aa0bf;
  --accent: #22d3ee;
  --accent-2: #3b82f6;
  --green: #34d399;
  --yellow: #fbbf24;
  --mono: "SF Mono", "Cascadia Code", Menlo, Consolas, "Liberation Mono", monospace;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", "PingFang SC", "Microsoft YaHei", sans-serif;
  line-height: 1.6;
}
.container { max-width: 1080px; margin: 0 auto; padding: 0 24px; }

/* language toggle: body[data-lang=en] hides .zh, and vice versa */
body[data-lang="en"] [data-i18n="zh"] { display: none; }
body[data-lang="zh"] [data-i18n="en"] { display: none; }

header {
  position: sticky; top: 0; z-index: 10;
  background: rgba(10, 15, 26, 0.85);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--panel-border);
}
.nav {
  display: flex; align-items: center; gap: 20px;
  padding: 14px 0;
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 18px; color: var(--text); text-decoration: none; }
.brand img { width: 28px; height: 28px; border-radius: 6px; }
.nav-links { margin-left: auto; display: flex; align-items: center; gap: 22px; }
.nav-links a { color: var(--text-dim); text-decoration: none; font-size: 14px; }
.nav-links a:hover, .nav-links a.is-active { color: var(--accent); }
.lang-btn {
  background: var(--panel); color: var(--text-dim);
  border: 1px solid var(--panel-border); border-radius: 6px;
  padding: 4px 12px; font-size: 13px; cursor: pointer; font-family: inherit;
}
.lang-btn:hover { color: var(--accent); border-color: var(--accent); }

.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 26px; border-radius: 8px; font-size: 15px; font-weight: 600;
  text-decoration: none; transition: transform 0.15s, box-shadow 0.15s;
}
.btn:hover { transform: translateY(-2px); }
.btn-primary {
  background: linear-gradient(90deg, var(--accent), var(--accent-2)); color: #051018;
  box-shadow: 0 4px 24px rgba(34, 211, 238, 0.35);
}
.btn-ghost { background: var(--panel); color: var(--text); border: 1px solid var(--panel-border); }
.btn-ghost:hover { border-color: var(--accent); }

section { padding: 64px 0; }
h2 { font-size: 30px; font-weight: 700; text-align: center; margin-bottom: 8px; }
.section-sub { text-align: center; color: var(--text-dim); margin-bottom: 44px; font-size: 15px; }

footer {
  border-top: 1px solid var(--panel-border); padding: 34px 0; text-align: center;
  color: var(--text-dim); font-size: 13px;
}
footer a { color: var(--accent); text-decoration: none; }

@media (max-width: 640px) {
  .nav-links a.nav-item { display: none; }
}