<div class="parent">

  <div class="child blue">

  </div>

  <div class="child pink">

  </div>  

</div>

.pink {

  background-color: pink;

}

​

.blue {

  background-color: blue;

}

​

.parent {

  background-color: gray;

  height: 400px;

}

​

.child {

  height: 100px;

  width: 100px;

}

​

​

​

​

​

​

​

body {

  min-height: 800px;

}