#toc {
  position: fixed;
  top: 20px;
  left: 20px;
  /* right: 20px; */
  padding: 10px;
  max-height: 90%;
  overflow-y: auto;
  display: none; /* 初始时不显示 */
  background-color: white;
  border-color: black;
  border: 1px solid;
  width: 200px;
}

#toc a {
  text-decoration: none;
  margin-bottom: 5px;
  display: block;
}

#toc a:hover {
  text-decoration: underline;
}

/* 媒体查询：在移动端隐藏目录 */
@media (max-width: 768px) {
  #toc {
    display: none;
  }
}