mozilla-release/testing/web-platform/tests/fullscreen/rendering/fullscreen-css-transition.html

<!DOCTYPE html>
<title>Transitions should not be stopped by going fullscreen</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<style>
  #trans {
    transition: color steps(1, end) 100s;
    color: green;
  }
</style>
<div id="trans">Should be green</div>
<script>
  async_test(t => {
    document.onfullscreenchange = t.step_func_done(() => {
      assert_equals(document.fullscreenElement, trans);
      assert_equals(getComputedStyle(trans).color, "rgb(0, 128, 0)", "Transition is in progress - still green");
    });
    trans.addEventListener('click', t.step_func(() => {
      trans.style.color = "red";
      trans.offsetTop;
      trans.requestFullscreen();
    }), {once: true});
    test_driver.click(trans);
  });
</script>