chromium/third_party/blink/web_tests/external/wpt/css/css-pseudo/backdrop-animate-002.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Test: A Web Animations on ::backdrop</title>
<link rel="help" href="https://fullscreen.spec.whatwg.org/#::backdrop-pseudo-element">
<link rel="match" href="backdrop-animate-002-ref.html">
<dialog id="target">Dialog contents</dialog>
<!-- This test fails on WPT.fyi with off-by-one on the green background (Chrome-only): -->
<meta name="fuzzy" content="maxDifference=0-1;totalPixels=0-472500">
<script>
const target = document.getElementById("target");
target.showModal();
target.animate({
  opacity: [0.1, 0.1],
  backgroundColor: ["green", "green"]
}, {
  pseudoElement: "::backdrop",
  duration: Infinity
});
</script>