css/css-backgrounds/child-move-reveals-parent-background.html

<!DOCTYPE html>
<html class="reftest-wait">
<title>Child moves and reveals previously obscured background of the parent</title>
<link rel="match" href="child-move-reveals-parent-background-ref.html">
<link rel="help" href="https://drafts.csswg.org/css-backgrounds">
<script src="/common/reftest-wait.js"></script>
<style>
  #parent {
    width: 150px;
    height: 150px;
    background-color: green;
  }
  #child {
    width: 150px;
    height: 150px;
    background-color: white;
    position: relative;
  }
</style>
<p>There should be a green square below.</p>
<div id="parent">
  <div id="child"></div>
</div>
<script>
  requestAnimationFrame(() => requestAnimationFrame(() => {
    child.style.left = '150px';
    takeScreenshot();
  }));
</script>