<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Test Reference</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<style>
div {
  width: 400px;
  height: 400px;
  background: blue;
  position: relative;
}
span {
  background: green;
  width: 200px;
  height: 200px;
  position: absolute;
  bottom: 0;
  left: 100px;
}
</style>
Should see a green square centered and at the bottom of the blue square.
<div><span></span></div>
