* {
	margin:0;
	padding:0;
}

html, body {
	height:100%;
	text-align:center;
	background-image:url('back.jpg');
}

.outer{
	width:1px;
	height:50%;
	margin-bottom:-225px; /* la mitad de la altura del div contenedor */
	float:left;
}

.capa{
	width:800px;
	height:450px;
	margin:auto;
	position:relative;
	clear:left;
	background-color:#ccc;
	border:solid 1px #666;
}