/* CSS Document */

#mydiv
	{
		position:absolute;
		top: 75%;
		left: 50%;
		width:40em;
		height:36em;
		margin-top: -19em; /*set to a negative number 1/2 of your height*/
		margin-left: -15em; /*set to a negative number 1/2 of your width*/
		padding: 20px;

	}