chromium/third_party/blink/web_tests/wpt_internal/css/css-fonts/size-adjust-ex-zoom.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>size-adjust should scale 'ex' correctly under zoom</title>
<link rel="help" href="https://drafts.csswg.org/css-fonts-5/#descdef-font-face-size-adjust">
<link rel="author" href="mailto:[email protected]">
<link rel="match" href="size-adjust-ex-zoom-ref.html">
<link rel="assert" title="size-adjust should scale 'ex' correctly under zoom">
<style>
@font-face {
  font-family: custom-font;
  src: local(Ahem), url(/fonts/Ahem.ttf);
  size-adjust: 40%;
  unicode-range: U+20, U+30-39; /* Digits and space */
}

.test {
  position: absolute;
  top: 0;
  left: 0;
  font-size: 20px;
}

.target {
  font-family: custom-font, sans-serif;
}

.square {
  display: inline-block;
  vertical-align: bottom;
  background-color: black;
  width: var(--l);
  height: var(--l);
}
</style>

<script>
if (window.testRunner)
  window.testRunner.setPageZoomFactor(3);
</script>

<div class="test">

<p>The computed 'font-size' value (i.e., 'em') should not be affected. But 'ex' should be scaled since it's measured from the actual glyph.</p>
<div class="target">
  <span class="square" style="--l: 1em"></span><span class="square" style="--l: 1ex"></span>
</div>

</div>