<!DOCTYPE HTML>
<style>
body {
  background-color: green;
}

#thediv {
  width: 300px;
  height: 100px;
  position: absolute;
  top: 20px;
  left: 20px;
  box-shadow: 3px 3px red;
}
</style>

<div id="thediv">Foo</div>