fontface-size-adjust-descriptor-ref.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Tests that the sizeAdjust attribute of FontFace works</title>
<script>
/* Load Ahem similarly to the testcase so that Gecko gives it the
   same antialiasing treatment. */
const ahem = new FontFace(
    'Ahem-normal',
    'local("Ahem"), url("/fonts/Ahem.ttf")');
document.fonts.add(ahem);
</script>
<style>
#target {
  font-family: "Ahem-normal";
  font-size: 40px;
  letter-spacing: 10px;
}
span {
  font-size: 50%;
}
</style>

<p>The first and fourth characters should be double-sized:</p>
<div id="target">
  F<span>oo</span>B<span>ar</span>
</div>

chromium/third_party/blink/web_tests/external/wpt/css/css-font-loading/fontface-size-adjust-descriptor-ref.html