<!DOCTYPE html>
<p>The word "FAIL" should not be seen below.</p>
<div style="position:relative; width:500px;">
    <div id="elm" style="background:blue; height:25em;">
        <div style="position:absolute; top:0; color:blue;">
            FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL FAIL
        </div>
    </div>
</div>
<script>
    document.body.offsetTop;
    document.getElementById("elm").style.marginLeft = "200px";
</script>