css/css-values/calc-rem-lang.html

<!doctype html>
<html lang="en"><!-- The lang is important! -->
<meta charset="utf-8">
<title>CSS Test: Calc with rem and relative units on the root element</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="help" href="https://drafts.csswg.org/css-values/#rem">
<link rel="help" href="https://drafts.csswg.org/css-values/#funcdef-calc">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1431031">
<link rel="match" href="calc-rem-lang-ref.html">
<style>
  html {
    font-size: calc(1rem + 1em);
  }
</style>
<p style="font-size: initial">You should see a green box twice-the-initial-font-size wide.</p>
<div style="width: 1em; height: 1em; background: green;"></div>
</html>