/* ===== 导航菜单 ===== */
.site-header {
 position: fixed;      /* 固定在顶部 */
  top: 0;
  left: 0;
  width: 100%;
  background: #222;     /* 深色背景 */
  padding: 10px 20px;
  z-index: 1000;
}

.site-header .logo {
  font-weight: bold;
  font-size: 1.2em;
  color: #fff;            /* 白字 */
  margin-right: 30px;     /* Logo 和菜单间距 */
  text-decoration: none;
}

.main-nav {
   display: flex;
  justify-content: flex-start; /* 靠左 */
  align-items: center;
  gap: 20px;                   /* 每个菜单间隔 */
}

.main-nav a {
  color: #fff;                 /* 白色字体 */
  text-decoration: none;
  font-weight: bold;
  font-size: 16px;
}

.main-nav a:hover {
  text-decoration: underline;
}