Funktioniert nicht:

Code: 
<html>
<head>
<style type="text/css">

body { 
	margin:0;
	padding:0; 
	background-color:rgb(0,0,0);
	font-family:tahoma; 
	font-size:10px; 
	color:white;
}

div {
	position:absolute;
	border:1px solid #888; 
	font-family:tahoma; 
	font-size:10px; 
}

#box {
	margin-left: auto;
	margin-right: auto;
}

</style>
</head>
<body>

<div id="box" style="width:500px; height:500px;">Test</div>

</body>
</html>