.absoluteCenter {
 /* Must manually set width/height */
 width:800px;
 height:500px;

 /* The magic centering code */
 margin:auto;
 position:absolute;
 top:0;bottom:0; /* Aligns Vertically - Remove for Horizontal Only */
 left:0;right:0; /* Aligns Horizontally - Remove for Vertical Only  */

 /* Prevent div from overflowing main window */
 max-width:100%;
 max-height:100%;
 overflow:auto;
}

/* IE 7 and Below */
:first-child+html .absoluteCenter,
* html .absoluteCenter {
 /* Place code here to override all above values, and add IE friendly centering */
}

.centerDiv{
     position: absolute;
     top: 50%;
     height: 400px;
     margin-top: -200px; /* Half of the height */
     left: 50%;
     width:800px;
     margin-left: -400px; /* Half of the width */
     border-radius: 5px;
     background:#111;
     padding:10px;
 }

html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    display: table
}
#content {
    display: table-cell;
    text-align: center;
    vertical-align: middle;
}

a { color: inherit; }