<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Test Reference</title>
<link rel="author" title="Rune Lillesveen" href="mailto:rune@opera.com">
<style>
  .refSquare {
    margin: 10px;
    width: 30px;
    height: 30px;
    background-color: green;
  }
</style>
<p>There should be three green 30x30 px squares below.</p>
<div>border-box</div>
<div class="refSquare"></div>
<div>padding-box</div>
<div class="refSquare"></div>
<duv>content-box</div>
<div class="refSquare"></div>