<nav> <ul> <li> <a>菜单1</a> <ul> 子菜单.... </ul> </li> </ul></nav>
<nav>
<ul>
<li>
<a>菜单1</a>
子菜单....
</ul>
</li>
</nav>
nav ul li:hover > ul { display: block;}
nav ul li:hover > ul {
display: block;
}
nav li ul { display: none; position: relative; z-index: 1;}
nav li ul {
display: none;
position: relative;
z-index: 1;
2 纯CSS的菜单
原文:http://www.cnblogs.com/yexiaodong/p/7254b425c9cc854348b5f9f184bc1f76.html