超简单实用的纯css下拉菜单代码，最多支持二级，一种下拉菜单的编写思路，从而更好的实现更多级的的导航菜单。
例子，纯css下拉菜单代码。
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type" content="text/html; charset=gb2312" />
<title>纯css下拉菜单代码</title>
<style>
#sddm
{
margin: 0 auto;
padding: 0;
z-index: 30;
background-color:#f4f4f4;
width: 480px;
height:23px;}
#sddm li
{margin: 0;
padding: 0;
list-style: none;
float: left;
font: bold 12px arial}
#sddm li a
{display: block;
margin: 0 1px 0 0;
padding: 4px 10px;
width: 60px;
background: #5970b2;
color: #fff;
text-align: center;
text-decoration: none}
#sddm li a:hover
{background: #49a3ff}
#sddm div
{position: absolute;
visibility: hidden;
margin: 0;
padding: 0;
background: #eaebd8;
border: 1px solid #5970b2}
#sddm div a
{position: relative;
display: block;
margin: 0;
padding: 5px 10px;
width: auto;
white-space: nowrap;
text-align: left;
text-decoration: none;
background: #eaebd8;
color: #2875de;
font: 12px arial}
#sddm div a:hover
{background: #49a3ff;
color: #fff}
</style>
<!-- dd menu -->
<script type="text/javascript">
<!--
var timeout = 500;
var closetimer= 0;
var ddmenuitem = 0;
// open hidden layer
function mopen(id)
{
// cancel close timer
mcancelclosetime();
// close old layer
if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';
// get new layer and show it
ddmenuitem = document.getelementbyid(id);
ddmenuitem.style.visibility = 'visible';
}
// close showed layer
function mclose()
{
if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';
}
// go close timer
function mclosetime()
{
closetimer = window.settimeout(mclose, timeout);
}
// cancel close timer
function mcancelclosetime()
{
if(closetimer)
{
window.cleartimeout(closetimer);
closetimer = null;
}
}
// close layer when click-out
document.onclick = mclose;
// -->
</script>
</head>
<body style="text-align:center">
<ul id="sddm">
<li><a href="#" onmouseover="mopen('m1')" onmouseout="mclosetime()">home</a>
<div id="m1" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">html dropdown</a>
<a href="#">dhtml dropdown menu</a>
<a href="#">javascript dropdown</a>
<a href="#">dropdown menu</a>
<a href="#">css dropdown</a>
</div>
</li>
<li><a href="#" onmouseover="mopen('m2')" onmouseout="mclosetime()">download</a>
<div id="m2" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">asp dropdown</a>
<a href="#">pulldown menu</a>
<a href="#">ajax dropdown</a>
<a href="#">div dropdown</a>
</div>
</li>
<li><a href="#" onmouseover="mopen('m3')" onmouseout="mclosetime()">order</a>
<div id="m3" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">visa credit card</a>
<a href="#">paypal</a>
</div>
</li>
<li><a href="#" onmouseover="mopen('m4')" onmouseout="mclosetime()">help</a>
<div id="m4" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">download help file</a>
<a href="#">read online</a>
</div>
</li>
<li><a href="#" onmouseover="mopen('m5')" onmouseout="mclosetime()">contact</a>
<div id="m5" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">e-mail</a>
<a href="#">submit request form</a>
<a href="http://www.jb200.com/" target="_blank">codefans.net</a>
</div>
</li>
</ul>
<div style="clear:both"></div>
<!--广告区域结束-->
</body>
</html>