DIV自动居中
<!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=utf-8" />
<title>无标题文档</title>
</head>
<body>
<style type="text/css">
<!--
div {
position:absolute;
top:50%;
left:50%;
margin:-100px 0 0 -100px;
width:200px;
height:200px;
border:1px solid red;
}
-->
</style>
<div></div>
</body>
</html>
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