<!DOCTYPE html>
<style>
::first-line { color: red }
.green { color: green }
</style>
<div class="green">
<span>This text should be green</span>
</div>
<script>
if (window.testRunner)
testRunner.waitUntilDone();
requestAnimationFrame(() =>
requestAnimationFrame(() => {
document.querySelector("span").className = "green";
if (window.testRunner)
testRunner.notifyDone();
}));
</script>