Vertically center a div inside another div

Center align a div not just horizontally but also vertically using display table cell.

HTML

<li><div class="wrapper">
    <div class="container">
        Center align a div using "<strong>display: table-cell</strong>"
    </div>
    <div class="container">
        Center align a div using "<strong>display: table-cell</strong>"
    </div>
</div>
</li>

CSS

.wrapper {
  display: table-cell;
  vertical-align: middle;
  text-align: center;
  width: 100%;
  height: 300px;
  border: 1px solid #555;
}

.container {
  display: inline-block;
  text-align: left;
  padding: 20px;
  border: 1px solid #cd0000;
}