* { box-sizing: border-box; }
body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: #f5f7fa;
  color: #111820;
  font-family: -apple-system, "PingFang SC", "Microsoft YaHei", sans-serif;
}
nav {
  padding: 20px 24px;
}
nav a {
  color: #2563eb;
  text-decoration: none;
  font-size: 14px;
}
main {
  flex: 1;
  max-width: 680px;
  margin: 0 auto;
  padding: 16px 24px 64px;
}
h1 {
  font-size: 32px;
  letter-spacing: -0.02em;
  margin: 24px 0 16px;
}
p {
  line-height: 1.8;
  color: #3a4550;
  font-size: 15px;
}
code {
  background: #e8edf3;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 13px;
}
.btn {
  display: inline-block;
  margin-top: 20px;
  background: #2563eb;
  color: #fff;
  padding: 11px 20px;
  border-radius: 8px;
  text-decoration: none;
  font-size: 14px;
}
.btn:hover { background: #1d4ed8; }
footer {
  border-top: 1px solid #e3e8ee;
  padding: 20px 24px;
  color: #66707a;
  font-size: 12px;
  text-align: center;
}