Vertically Center Element
<!-- http://html5hub.com/centering-all-the-directions/ -->
<style>
#ex3_container {
width:200px;
height:200px;
background-color:yellow;
position:relative;
}
#ex3_content {
left:50%;
top:50%;
transform:translate(-50%,-50%);
-webkit-transform:translate(-50%,-50%);
background-color:gray;
color:white;
position:absolute;
}
</style>
<div id="ex3_container">
<div id="ex3_content">Hello World</div>
</div>