Because our wiki is on a wiki farm, we occasionally get a GlobalSiteNotice set, and it's usually just some text in {| class="wikitable ... which appears at the top of all pages. Class wikitable has a margin: 1em 0; which seems pretty benign. However, because it's the first element, it stacks all the way up to div#content-wrapper, giving it a margin too. This is all according to spec.

Unfortunately, this causes the header to float on top of the content (1em down, of course). I think the solution would be to create a new block formatting context for the content box, either by adding overflow:auto or display: inline-block to either of #wikipage-content or #site-notice. Probably inline-block, because Refreshed isn't really targeting ancient browsers.