<!DOCTYPE html>
<style>
.parent {
  width: 100px;
  height: 100px;
  background-color: rgb(100, 100, 0);
}
.container {
  width: 100px;
  height: 100px;
  background-color: rgb(100, 0, 100);
}
</style>
<body>
  <div class='parent'>
    <div class='container'></div>
  </div>
</body>