<n* class="dropdown-menu">
  <ul>
    <li><a href="#">首页</a></li>
    <li class="has-submenu">
      <a href="#">产品</a>
      <ul class=&quot;submenu">
        <li><a href="#">产品一</a></li>
        <li><a href="#">产品二</a></li>
        <li><a href="#">产品三</a></li>
      </ul>
    </li>
    <li><a href="#">关于我们</a></li>
  </ul>
</n*>

.dropdown-menu ul {
  list-style: none;
  margin: 0;
  padding: 0;
  background: #f8f8f8;
}
<p>.dropdown-menu > ul > li {
display: inline-block;
position: relative;
}</p><p>.dropdown-menu a {
display: block;
padding: 10px 15px;
text-decoration: none;
color: #333;
}</p><p>/<em> 隐藏子菜单 </em>/
.submenu {
display: none;
position: absolute;
top: 100%;
left: 0;
background: #fff;
border: 1px solid #ddd;
min-width: 120px;
}</p><p>.submenu li {
display: block;
}</p><p>/<em> 悬停时显示子菜单 </em>/
.has-submenu:hover .submenu {
display: block;
}</p><p>/<em> 可选：添加简单过渡效果 </em>/
.submenu {
opacity: 0;
visibility: hidden;
transition: opacity 0.2s, visibility 0.2s;
}</p><p>.has-submenu:hover .submenu {
display: block;
opacity: 1;
visibility: visible;
}</p>