Centering vertically with CSS can be a pain. Check out Dead Centre. It requires an extra container 'horizon' to know where the vertical center is, and unfortunately you must know the dimensions of the content you want centered so that you can offset it.
Goes something like this...
body {
margin: 0px
}
#horizon {
text-align: center;
position: absolute;
top: 50%;
left: 0px;
width: 100%;
height: 1px;
overflow: visible;
visibility: visible;
display: block
}
#content {
margin-left: -125px;
position: absolute;
top: -35px;
left: 50%;
width: 250px;
height: 70px;
visibility: visible
}
<body>
<div id="horizon">
<div id="content">
content you want centered
</div>
</div>
</body>
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