I need for a certain dynamic element to always appear on top of another element, no matter what order in the DOM tree they are. Is this possible? I've tried z-index (with position: relative), and it doesn't seem to work. I hate to be vague, but this is the simplest way I can think of asking this question without explaining its purpose ad nauseum.

So, to recap, I need

<div class="a">
    <div class="b"></div>
</div>

<div class="b">
    <div class="a"></div>
</div>

To display exactly the same when rendered. And for flexibility purposes (I'm planning on distributing a plugin that needs this functionality), I'd really like to not have to resort to absolute or fixed positioning.