纯CSS实现三级导航下拉菜单

<!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>
</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>