<!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=gb2312" />
<title>无标题文档</title>
<style>
.juzhong{
position:absolute;
top:50%;
left:50%;
margin-left:-150px;
margin-top:-100px;
width:300px;
height:200px;
background-color:orange;
}
</style>
<body>
<div class="juzhong">Login</div>
</body>
</html> 这样就居中了..可以做登录呀...遮罩层呀神马乱七八糟的都行....