<div class="outer-div"><div class="mid-div"><div class="center-div"></div></div></div>
body
{
  background-color: #fcfcfc;
}
.outer-div
{
  display: table;
  position: absolute;
  height: 100%;
  width: 100%;
}
.mid-div
{
  display: table-cell;
  vertical-align: middle;
}
.center-div
{
  margin: 0 auto;
  width: 300px;
  height: 100px;
  background-color: #ddd;
  border-radius: 3px;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.