div下上居中css方法 _HTML/CSS

div上下居中css方法

<!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" />
<style>
.test{
width:500px;
height:500px;
position:absolute;
top:50%;
left:50%;
margin:-250px 0 0 -250px; 
background:gray;
}
</style>
<title>无标题文档</title>
</head>
<body>
<div class="test">
</div>
</body>
</html>