<!DOCTYPE html>
<style>
#a, #c {
width:25px;
height:50px;
background: blue;
float: left;
}
</style>
<p>There should be a blue <em>square</em> below.</p>
<div>
<div id="a"></div><div id="b"></div><div id="c"></div>
</div>
<script>
document.body.offsetTop;
document.getElementById('b').style.display = 'inline-block';
</script>