To horizontally and vertically center an element in css: http://css-tricks.com/centering-percentage-widthheight-elements/

center.css

/*
 * To horizontally and vertically center an element in css:
 * http://css-tricks.com/centering-percentage-widthheight-elements/
 */

.center {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 20em;
  height: 20em;
}