PHP导航下拉菜单的实现如此简单

<style> 
#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> 
<div class="header_continer002"> 
<div class="header"> <img class="logo" src="images/logo.jpg" /> <span class="pos_01">服务热线<br /> 
400-691-6006</span> <span class="pos_02"> <a href="http://u.youku.com/user_show/id_UMzMxNDI5MTgw.html" target="_blank"><img src="images/top_pic01.jpg" /></a> 
<div style="margin-top:5px;"> <a href="http://weibo.com/tcdd" target="_blank"><img src="images/top_pic02.jpg" /></a></div> 
</span> 
<ul class="nav" onmouseout="hide_sub()" id="sddm"> 
<li><a href="/">首页</a></li> 
<li><a href="/plus/list.php?tid=1" onmouseover="mopen('m1')" onmouseout="mclosetime()">关于我们</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="/plus/list.php?tid=2" onmouseover="mopen('m2')" onmouseout="mclosetime()">新闻中心</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="/plus/list.php?tid=3" onmouseover="mopen('m3')" onmouseout="mclosetime()">解决方案</a> 
<div id="m3" 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="/plus/list.php?tid=4" onmouseover="mopen('m4')" onmouseout="mclosetime()">产品展示</a> 
<div id="m4" 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="/plus/list.php?tid=5" onmouseover="mopen('m5')" onmouseout="mclosetime()">支持与下载</a> 
<div id="m5" 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="/plus/list.php?tid=6" onmouseover="mopen('m6')" onmouseout="mclosetime()">人才招聘</a> 
<div id="m6" 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="/plus/list.php?tid=7" onmouseover="mopen('m7')" onmouseout="mclosetime()">联系我们</a> 
<div id="m7" 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> 
</ul> 
</dl> 
</div> 
</div> 
</div>