css玩起来也挺有意思，在这里放个抄袭转载来的 代码示例
<!DOCTYPE html>
<html>
<head>
<title>test</title>
<style type = "text/css">
/*设置通配符样式*/
*{
margin:0;
padding:0;
}
body{
font-size:12px;
}
ul{
list-style:none;
}
a{
text-decoration:none;
}
/*设置二级导航样式*/
.nav {
width:500px;
height:30px;
background-color:#b4b4b4;
/*导航栏居中*/
margin:auto;
}
.nav ul li {
width:100px;
height:30px;
float:left;
position:relative;
}
.nav ul li a {
display:block;
width:96px;
border:2px solid gray;
height:26px;
line-height:26px;
text-align:center;
}
.nav ul li a:hover {
background-color:yellow;
}
/*设置一级导航样式*/
.nav ul li ul{
display:none;
}
.nav ul li:hover ul{
display:block;
width:100px;
position:absolute;
top:30px;
left:0;
background-color:white;
}
.nav ul li:hover ul li a{
display:block;
width:96px;
height:26px;
line-height:26px;
border:2px solid gray;
text-align:center;
}
.nav ul li:hover ul li a:hover{
background-color:orange;
}
/*设置三级导航样式*/
.nav ul li:hover ul li ul {
display:none;
}
.nav ul li:hover ul li:hover ul{
display:block;
width:100px;
position:absolute;
top:0px;
left:100px;
background-color:#b4b4b4;
}
.nav ul li:hover ul li:hover ul li {
width:100px;
height:30px;
}
.nav ul li:hover ul li:hover ul li a {
display:block;
width:96px;
height:26px;
line-height:26px;
border:2px solid gray;
text-align:center;
}
.nav ul li:hover ul li:hover ul li a:hover {
background-color:#00CC00;
}
.nav ul li:hover ul .nav_jw ul {
display:none;
}
.nav ul li:hover ul .nav_jw:hover ul{
display:block;
width:100px;
position:absolute;
top:0px;
left:-100px;
background-color:#b4b4b4;
}
.nav ul li:hover ul .nav_jw:hover ul li {
width:100px;
height:30px;
}
.nav ul li:hover ul .nav_jw:hover ul li a {
display:block;
width:96px;
height:26px;
line-height:26px;
border:2px solid gray;
text-align:center;
}
.nav ul li:hover ul .nav_jw:hover ul li a:hover {
background-color:#00CC00;
}
</style>
<meta charset="utf-8">
</head>
<body>
<div class = "nav">
<ul>
<li><a href = "#">一级导航</a>
<ul>
<li><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
<li><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
<li><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
</ul>
</li>
<li><a href = "#">一级导航</a>
<ul>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
</ul>
</li>
<li><a href = "#">一级导航</a>
<ul>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
</ul>
</li>
<li><a href = "#">一级导航</a>
<ul>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
<li><a href = "#">二级导航</a></li>
</ul>
</li>
<li><a href = "#">一级导航</a>
<ul>
<li class="nav_jw"><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
<li class="nav_jw"><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
<li class="nav_jw"><a href = "#">二级导航</a>
<ul>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
<li><a href = "#">三级导航</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</body>
</html>
