<div class="parent">
  <div class="child"></div>
</div>
.parent {
  background-color: red;
  width: 300px;
  height: 100px;
}
.child {
  width: 160px;
  height: 0;
  padding-top: 56.25%;
  background-color: blue;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.