<!doctype html>
<title>CSS Test reference</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<style>
:root {
  font-size: 2em;
}

div {
  width: 10rem;
  height: 10rem;
  background: green;
}
</style>
<div></div>
