Is the browser supports it, using translate is powerful.
position: absolute;
background-color: red;
width: 70%;
height: 30%;
/* The translate % is relative to the size of the div and not the container*/
/* 21.42% = ( (100%-70%/2) / 0.7 ) */
/* 116.666% = ( (100%-30%/2) / 0.3 ) */
transform: translate3d( 21.42%, 116.666%, 0);