:root {
  --text: #1d1d1f;
  --muted: #6e6e73;
  --accent: #0066cc;
  --bg: #ffffff;
  --bg-soft: #f5f5f7;
  --border: #e5e5ea;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

/* Language switching: html[data-lang] decides which content shows */
html[data-lang="en"] .zh { display: none !important; }
html[data-lang="zh"] .en { display: none !important; }

#lang-toggle {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 3px 12px;
  font-size: 13px;
}
#lang-toggle:hover { border-color: var(--accent); }

body {
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.75;
  font-size: 16px;
}

header {
  border-bottom: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.9);
  position: sticky;
  top: 0;
  backdrop-filter: blur(10px);
}

.nav {
  max-width: 780px;
  margin: 0 auto;
  padding: 14px 20px;
  display: flex;
  align-items: center;
  gap: 24px;
  flex-wrap: wrap;
}

.nav .brand { font-weight: 600; font-size: 17px; margin-right: auto; }

.nav a { color: var(--muted); text-decoration: none; font-size: 14px; }
.nav a:hover, .nav a.active { color: var(--accent); }

main { max-width: 780px; margin: 0 auto; padding: 48px 20px 80px; }

h1 { font-size: 32px; line-height: 1.25; margin-bottom: 8px; }

.meta { color: var(--muted); font-size: 14px; margin-bottom: 36px; }

h2 { font-size: 21px; margin: 36px 0 12px; }

p, li { color: #333336; margin-bottom: 10px; }

ul, ol { padding-left: 24px; margin-bottom: 16px; }

a { color: var(--accent); }

.card {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px 24px;
  margin: 16px 0;
}

.card h3 { font-size: 17px; margin-bottom: 6px; }

.grid { display: grid; gap: 16px; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); margin-top: 32px; }
.grid a.card { display: block; text-decoration: none; color: inherit; transition: border-color 0.15s; }
.grid a.card:hover { border-color: var(--accent); }
.grid a.card p { color: var(--muted); font-size: 14px; margin: 0; }

footer {
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 13px;
  text-align: center;
  padding: 24px 20px;
}