css3-values/initial-vs-rem.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Initial</title>
<style type="text/css">
:root {font-size: 30px;}
div#d01 {font-size: 66.6667%;}
p#p01 {font-size: 1rem;}
p#p02 {font-size: initial;}
</style>
</head>
<body>

<p>
This is paragraph outside the <code>div</code>.  Its font size should be 30 pixels.
</p>

<div id="d01">
This is a <code>div</code> with an <code>id</code> of <code>d01</code>.  Its font size should be 20 pixels.

<p id="p01">
This is a <code>p</code> with an <code>id</code> of <code>p01</code>.  Its font size should be 30 pixels.
</p>
<p id="p02">
This is a <code>p</code> with an <code>id</code> of <code>p02</code>.  Its font size should be user-default size (generally 16px, but your user agent may vary).
</p>

</div>

<a href="http://www.w3.org/TR/css3-values">Specification</a>

</body>
</html>