全屏显示 在IE7下body会有滚动条出现解决办法

全屏显示 在IE7下body会有滚动条出现
<!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" />
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>demo-非全屏-使用box-sizing:content-box</title>
<style>
*{padding:0;margin:0;border:none;}
body{width:100%;height:100%;overflow:hidden;}
.pr{position:relative;}
.pa{position:absolute;}
.pf{position:fixed;}
.of-h{overflow:hidden;}
.of-a{overflow:auto;}
.of-s{overflow:scroll;}
.wrap{width:100%;height:100%;}
.header{width:100%;height:100px;background:#ccc;z-index:1;}
.content{width:100%;height:auto;top:100px;bottom:100px;background:#03C;z-index:0;}
.footer{bottom:0;width:100%;height:100px;background:#ccc;z-index:1;}
</style>

</head>

<body class="pa">
<div class="wrap pr" style="width:90%;margin:0 auto;">
     <div class="header pa of-h">header 高度100px z-index:1</div>
     <div class="content pa of-a">
         <div>content z-index:0<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />...<br />content z-index:0<br /></div>
        </div>
     <div class="footer pa of-h">footer 高度100px z-index:1</div>
</div>
</body>
</html>


大伙看看哪里出问题了,是代码问题还是ie7就是这样子的?
------解决方案--------------------
给html添加同样的样式
html,body{width:100%;height:100%;overflow:hidden;}