:root {
  --bg: #f6f7f9;
  --card: #ffffff;
  --fg: #1a1d21;
  --muted: #6b7280;
  --line: #e5e7eb;
  --accent: #1677ff;
}
* { box-sizing: border-box; }
body {
  margin: 0; min-height: 100vh;
  display: grid; place-items: center;
  background: var(--bg); color: var(--fg);
  font: 15px/1.7 -apple-system, "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
}
.card {
  background: var(--card); border: 1px solid var(--line); border-radius: 14px;
  padding: 32px 36px; max-width: 560px; box-shadow: 0 8px 30px rgba(0,0,0,.06);
}
h1 { margin: 0 0 4px; font-size: 22px; }
.sub { margin: 0 0 20px; color: var(--muted); font-size: 13px; }
ul { margin: 0 0 20px; padding-left: 18px; }
li { margin: 4px 0; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
code { background: #f1f3f5; padding: 1px 6px; border-radius: 5px; font-size: 13px; }
.hint { margin: 0; color: var(--muted); font-size: 12.5px; border-top: 1px solid var(--line); padding-top: 14px; }