A CodePen by Robert Pearce.

index.html

<div class="wrapper">
  <div class="box"></div>
  <div class="box content">Some text</div>
</div>

style.css

html, body {
  height: 101%;
}

.wrapper {
  width: 100%;
  height: 100%;
  text-align: center;  
  background-color: #ccc;
}

.box {
  display: inline-block;
  vertical-align: middle;
  height: 100%;
}

.content {
  background: #fff;
  height: auto;
}