<div class="outer-box">
  <div class="inner-box">
  </div><!-- .inner-box -->
</div><!-- .outer-box -->
.outer-box {
  width: 300px;
  height: 300px;
  background: black;
}
.inner-box {
  width: 150px;
  height: 150px;
  background: red;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.