Ciao, ho bisogno di avere un box alto 100%, ma con lo strict non funziona!!

Come si fa?

Grazie

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link href="prova.css" rel="stylesheet" type="text/css">
</head>

<body>

<div id="box"></div>
	
</body>
</html>
codice:
body {
	padding:0px;
	margin:0px;
	height:100%;
}

#box {
	position:relative;
	width:100%;
	height:100%;
	background:#FFFF00;
}