css/css-values/ex-unit-004.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Values and Units Test: support for the ex unit</title>
<link rel="author" title="Jonathan Kew" href="mailto:jkew@mozilla.com">
<link rel="help" href="https://drafts.csswg.org/css-values-3/#font-relative-lengths">
<link rel="help" href="https://www.w3.org/TR/css-fonts-3/#first-available-font">
<link rel="match" href="reference/ex-unit-004-ref.html">
<meta name="assert" content="The ex unit equals the x-height of the first available font if it has reliable metrics for the x-height.">
<style>
@font-face {
  font-family: ExTestNoSpace;
  src: url(resources/ExTest-NoSpace.woff);
}
div {
  height: 10px;
  background-color: blue;
  margin-top: 10px;
  font-size: 80px;
  width: 10ex;
}
.test {
  font-family: ExTestNoSpace, Arial, sans-serif;
}
.ref {
  font-family: Arial, sans-serif;
}
</style>
<p>The test passes if there are two blue rectangles of equal length.</p>
<!-- ExTest is a font whose OS/2 table's sxHeight field is set to an
     eighth of the font's units per em, but it does not support the
     <space> character and therefore is not valid as "first available font"
     per CSS Fonts, and must NOT be used as the basis of the 'ex' unit. -->
<div class="test"></div>
<div class="ref"></div>