html, body {
	height: 100%;
	overflow: hidden;
}
.center550400 {
	width: 550px;
	height: 400px;
	text-align: center;
	position: absolute;
	left: 50%;
	top: 50%;
	margin-left: -275px; 
	/* Half the width of the DIV tag which is 50 pixels */
	margin-top: -200px; 
	/* Half the height of the DIV tag which is also 50 pixels */
}
.center420280 {
	width: 420px;
	height: 280px;
	text-align: center;
	position: absolute;
	left: 50%;
	top: 50%;
	margin-left: -210px; 
	/* Half the width of the DIV tag which is 50 pixels */
	margin-top: -140px; 
	/* Half the height of the DIV tag which is also 50 pixels */
}