JS弹出居中的DIV

JS部分:
<script language="javascript">
//******************************************************
function controlDiv(DivID,divCase){
var divs=document.getElementById(DivID); 
var v_left=(document.body.clientWidth-300)/2 + document.body.scrollLeft; //divs.clientWidth
var v_top=(document.body.clientHeight-divs.clientHeight)/2 + document.body.scrollTop;
if(divCase==1){
divs.style.left=v_left+'px';
divs.style.top=v_top+'px';
divs.style.display="block"; //显示DIV
}else if(divCase==2)
divs.style.display="none"; //屏蔽DIV
else
   divs.innerHTML=divCase; //输出HTML文本到DIV
}
//******************************************************
</script>

HTML部分:
<style type="text/css">
<!--
body,td,th {
font-size: 12px;
margin:0
}
#msgDiv{ position:absolute; display:none; width:300px; background:#FFF; border: #DDD 8px solid; z-index:2009}
#msgDiv h1{ margin:0px; padding:5px 3px 0px 3px; height:20px; background:#F4FAFF; font-weight:normal; font-size:12px;}
#msgDiv h1 span{ float:right}
-->
</style>
<div align="center">
<p>&nbsp;</p>
<p><a href="#" onclick="controlDiv('msgDiv',1)">点击弹出</a></p>
</div>
<p>&nbsp;</p>
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<div align="center"><a href="#" onclick="controlDiv('msgDiv',1)">点击弹出</a></div>
<div id="msgDiv">
<h1><span>[<a href="#" onclick="controlDiv('msgDiv',2)">关闭</a>]</span>弹出窗口</h1>
    <div align="center"><br />
    content<br />
    </div>
</div>

本文出处：http://hi.baidu.com/jaes7107/item/848e77c486b8092c47d5c07a