chromium/third_party/blink/web_tests/external/wpt/fullscreen/rendering/backdrop-object.html

<!DOCTYPE html>
<html class=reftest-wait>
<title>::backdrop for a fullscreen object element</title>
<link rel=match href="backdrop-object-ref.html">
<link rel=help href="https://github.com/w3c/csswg-drafts/issues/6939">
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>

<style>
object::backdrop {
  background: blue;
}
</style>
<object width="200" type="image/svg+xml" data="../../images/100px-green-rect.svg"></object>
<script>
const object = document.querySelector("object");
Promise.all([
    new Promise((resolve, reject) => document.addEventListener("fullscreenchange", resolve)),
    new Promise((resolve, reject) => object.addEventListener("load", resolve))
]).then(() => document.documentElement.classList.remove('reftest-wait'));

test_driver.bless('fullscreen', () => object.requestFullscreen());
</script>