html, body {
	height:100%;
	width:100%;
	margin:0;
	padding:0;
}

#box {
	position:absolute;
	right:25%;
	left:25%;
	width:50%;
	background: transparent;
	border:0px solid #999999;
	margin-left:auto;
	margin-right:auto;
	height:60%;
	margin-top: 20%;
	margin-bottom: 20%;
}

<!--[if gte IE 5.5]>
   <style type="text/css">
   <!--
   div{height:70%;}
<![endif]-->