<!DOCTYPE html>
<style>
p:first-child {
    display:none;
}
</style>
<script>
if (window.testRunner)
    testRunner.dumpAsText();
</script>
<p>You should see the word 'PASS' below:</p>
<div id="container">
    <p>PASS</p>
</div>
<script>
container.offsetTop;
container.insertBefore(document.createElement("p"), container.querySelector("p"));
</script>