margin-top: -250px; /*set to a negative number 1/2 of your height*/
margin-left: -225px; /*set to a negative number 1/2 of your width*/
border: 1px solid #ccc;
margin-top: -250px; /*set to a negative number 1/2 of your height*/
margin-left: -225px; /*set to a negative number 1/2 of your width*/
border: 1px solid #ccc;