rc="/resources/testharnessreport.js"></script>
<style>
.before::before,
.after::after,
.backdrop::backdrop {
  font: 25px/1 "custom font", monospace;
  background: linear-gradient(45deg, red, blue);
  background-size: 1ch 1ch;
}
</style>

<div class="container before"></div>
<div class="container after"></div>
<dialog class="container backdrop"></dialog>

<script>
function parseBackgroundSizeInPx(element, pseudoElement) {
  const x = getComputedStyle(element, pseudoElement).backgroundSize.split(' ')[0];
  i