HTML + CSS下拉菜单

<ul>
  <li><a href="#">菜单项1</a></li>
  <li><a href="#">菜单项2</a></li>
  <li><a href="#">菜单项3</a></li>
</ul>

ul {
  list-style-type: none;
  background-color: #f1f1f1;
  padding: 0;
}

li {
  display: inline-block;
}

li a {
  display: block;
  color: #333;
  text-decoration: none;
  padding: 10px 20px;
}

li:hover {
  background-color: #ddd;
}

li:hover ul {
  display: block;
}

ul ul {
  display: none;
  position: absolute;
  background-color: #fff;
  border: 1px solid #ccc;
}

ul ul li {
  display: block;
}

li:hover ul {
  display: block;
}