Last updated on December 23, 2015
#container {
width: 400px; /* here you put the width that you need */
height: 200px; /* here you put the height that you need */
position:absolute;
left:50%;
top:50%;
margin-left:-200px; /* this number always to be the width divided two in negative */
margin-top:-100px; /* this number always to be the height divided two in negative */
}