<div clss="s3-relative">
  <div class="s3-absolute">
    The centered absolute div under relative div
  </div>
</div>

.s3-relative{
	position:relative;
	width:100%;
	height:100%;
}
.s3-absolute{
	position:absolute;
	top:0;
	right:0;
	bottom:0;
	left:0;
	width:50%;
	height:50%;
	margin:auto;
  padding:1em 0;
  background-color:#000;
  color:#fff;
  text-align:center;
}