我的效果：
我的导航代码：问题，下拉菜单不出来，被导航栏高度限制
<!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>简洁的纯CSS下拉菜单代码</title>
<style>
#sddm
{ margin: 0 auto;
padding: 0;
z-index: 30;
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;
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 = 100;
var closetimer = 10;
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="网页地址" onmouseover="mopen('m1')" onmouseout="mclosetime()">主页</a>
<div id="m1" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
</div>
</li>
<li><a href="网页地址" onmouseover="mopen('m2')" onmouseout="mclosetime()">动态</a>
<div id="m2" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a target="_blank" href="http://www.baidu.com">子菜单1</a>
<a target="_blank" href="http://www.baidu.com">子菜单2</a>
<a target="_blank" href="http://www.baidu.com">子菜单3</a>
</div>
</li>
<li><a href="网页地址" onmouseover="mopen('m3')" onmouseout="mclosetime()">板块</a>
<div id="m3" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">Visa Credit Card</a>
<a href="#">Paypal</a>
</div>
</li>
<li><a href="网页地址" onmouseover="mopen('m4')" onmouseout="mclosetime()">关于</a>
<div id="m4" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">Download Help File</a>
<a href="#">Read online</a>
</div>
</li>
<li><a href="网页地址" onmouseover="mopen('m5')" onmouseout="mclosetime()">关于</a>
<div id="m5" onmouseover="mcancelclosetime()" onmouseout="mclosetime()">
<a href="#">E-mail</a>
<a href="#">Submit Request Form</a>
<a href="http://www.codefans.net/" target="_blank">codefans.net</a>
</div>
</li>
</ul>
</body>
</html>
