<div id="box"></div>
*{
padding: 0px;
margin: 0px;
}
html,body{
width: 100%;
height: 100%;
}
div{
height: 100%;
}
#box{
width: 200px;
height: 200px;
background-color: red;
position: relative;
top: 50%;
left: 50%;
-webkit-transform: translateX(-50%);
margin-top: -100px;
}