[code] Horizontal and vertical center for a div in CSS

#centerDiv {
  position: absolute;
  left: 50%;
  width: /* width of your div, say 800px */;
  margin-left: /* half width of your div and make it negative, so would be -400px */

  top: 50%;
  height: /* height of your div, say 600px */;
  margin-top: /* half heigt of your div and make it negative, so would be -300px */
}

Reference from here