chromium/third_party/blink/web_tests/external/wpt/css/css-contain/contain-paint-change-opacity.html

<!DOCTYPE html>
<html class="reftest-wait">
<link rel="help" href="https://drafts.csswg.org/css-contain-2/#contain-property">
<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
<script src="/common/reftest-wait.js"></script>
<script src="/common/rendering-utils.js"></script>
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div style="width: 100px; background: red">
  <div id="container" style="contain: paint; opacity: 0.1">
    <div style="height: 100px; background: green; position: relative"></div>
  </div>
</div>
<script>
waitForAtLeastOneFrame().then(() => {
  container.style.opacity = 1;
  takeScreenshot();
});
</script>
</html>