.outer {
display: table;
position: absolute;
top: 0;
left: 0;
height: 100%;
width: 100%;
}
.middle {
display: table-cell;
vertical-align: middle;
}
.inner {
margin-left: auto;
margin-right: auto;
width: 400px;
/*whatever width you want*/
}
<div class="outer">
<div class="middle">
<div class="inner">
<h1>The Content</h1>
<p>Once upon a midnight dreary...</p>
</div>
</div>
</div>