body {
  max-width: 72ch;
  margin: 2em auto;
  padding: 0 1em;

  font-family: "PingFang SC", serif;
  font-size: 16px; /* ← 关键：明确基准字号 */
  line-height: 1.6;

  color: #000;
  background: #fff;
}

h1,
h2,
h3 {
  font-weight: normal;
}

h1 {
  text-align: center;
}

.small {
  font-size: 12px; /* ← 不再用 x-small，用绝对值 */
}

ul {
  padding-left: 1.5em;
}

li {
  margin: 0.3em 0;
}

a,
a:visited {
  color: #00f; /* 经典学术蓝 */
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

pre {
  background-color: #f5f5f5;
  padding: 15px;
  border-radius: 4px;
  margin: 15px 0;
  overflow-x: auto;
}
code {
  background-color: #f5f5f5;
  padding: 2px 6px;
  border-radius: 3px;
  font-size: 14px;
}