鼠标经过时弹出下拉菜单

<style type="text/css">
#cssdropdown, #cssdropdown ul {
padding: 0;
margin: 0;
list-style: none;
}
#cssdropdown li {
float: left;
position: relative;
}
.mainitems{
border: 1px solid black;
background-color: #FFEEC6;
}
.mainitems a{
margin-left: 6px;
margin-right: 8px;
text-decoration: none;
}
.subuls{
display: none;
10em;
position: absolute;
top: 1.2em;
left: 0;
background-color: lightyellow;
border: 1px solid black;
}
.subuls li{
100%;
}
.subuls li a{
text-decoration: underline;
}
#cssdropdown li>ul { /* to override top and left in browsers other than IE, which will position to the top right of the containing li, rather than bottom left */
top: auto;
left: auto;
}
#cssdropdown li:hover ul, li.over ul { /* lists nested under hovered list items */
display: block;
}
#restofcontent { /*wrap rest of content of the page inside this div*/
clear: left;
}
</style>
<script type="text/javascript"><!--//--><![CDATA[/><!--
startList = function() {
if (document.all&&document.getElementById) {
cssdropdownRoot = document.getElementById("cssdropdown");
for (i=0; i<cssdropdownRoot.childNodes.length; i++) {
node = cssdropdownRoot.childNodes[i];
if (node.nodeName=="LI") {
node.onmouseover=function() {
this.className+=" over";
}//欢迎来到站长特效网，我们的网址是www.zzjs.net，很好记，zz站长，js就是js特效，本站收集大量高质量js代码，还有许多广告代码下载。
node.onmouseout=function() {
this.className=this.className.replace(" over", "");
}
}
}
}
}
if (window.attachEvent)
window.attachEvent("onload", startList)
else
window.onload=startList;
//--><!]]>
</script>
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<ul id="cssdropdown">
<li class="mainitems">
<a href="http://www.zzjs.net">站长特效网</a>
<ul class="subuls">
<li><a href="<#ZC_BLOG_HOST#>?cat=1">zzjs</a></li>
<li><a href="<#ZC_BLOG_HOST#>?cat=2">网页特效</a></li>
<li><a href="<#ZC_BLOG_HOST#>?cat=11">广告代码</a></li>
<li><a href="<#ZC_BLOG_HOST#>">RSS订阅</a></li>
</ul>
</li>
<li class="mainitems">
<a href="http://www.alixixi.com/">阿里西西</a>
<ul class="subuls" style=" 15em">
<li><a href="http://www.alixixi.com">网站首页</a></li>
<li><a href="http://cool.alixixi.com">酷站欣赏</a></li>
<li><a href="http://js.alixixi.com">网页特效</a></li>
</ul>
</li>
</ul>