分享一个遮罩层 网上的例子复杂的很 其实很简单

<!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 content="text/html; charset=utf-8" http-equiv="Content-Type"/>
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7"/>
<link href="box/global.css" rel="stylesheet" type="text/css"/>
<meta name="keywords" content=""/>
<meta name="description" content=""/>
<title>jquery</title>
<script type="text/javascript"  src="box/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
    $("#boxA").height($(window).height()).width($(window).width()); 
$(window).resize(function(){
                 $("#boxA").height($(window).height()).width($(window).width()); 
 })  
    });
</script>
<style></style>
</head>
<body>
<div id="boxA" style="background:#FF0000; filter:alpha(opacity=50); opacity:0.5;"></div>
</body>
</html>为了换点积分 谢谢大家理解