.tab {
    width:500px;
    height:300px;
    position:fixed;
    margin-left:-150px; 
    margin-top:-150px;  
    top:50%;
    left:40%;
}
img.bg {
	/* Set rules to fill background */
	min-height: 100%;
	min-width: 1024px;
	
	/* Set up proportionate scaling */
	width: 100%;
	height: auto;
	
	/* Set up positioning */
	position: fixed;
	top: 0;
	left: 0;
}
div#container {
	/* This is the only important rule */
	/* We need our content to show up on top of the background */
	position: relative; 
}