lucy24 - 11:04 pm on Oct 3, 2012 (gmt 0)

Tangential answer: What's the purpose of these three lines?
position:absolute;
top:0px;
width:100%;
The width of a div is always 100% unless you've set it to something else. If it's the first thing in the html, it will go to the top of the page without further instructions. That's assuming your boilerplate has set a 0 top margin for the body (and html, if you want to go belt-and-suspenders).

I've known browsers to be snarky about the "margin: auto" setting, especially in combination with specific numbers, whether em or percent. Technically it should make no difference whatsoever, but see what happens if you say explicitly
{margin-top: 0; margin-right: auto;}
et cetera.