The new MediaWiki theme looks good, though the popupToolGroup (a toolbar element, ref. demo) should have a hover (and probably active) state when someone mouses over or clicks the element. Apex has both a hover state and an active state, and the current editor has both as well. Adding such a state would make the editor toolbar seem more responsive.
However, this is inconsistent with the hover behavior of the other buttons, so it's a valid question whether it's a good idea or not to add a preferential hover state to the popup tool group. However, I think it should have an active state, since other toolbar buttons themselves have an active state when activated, so adding one to the popup tool group when the popup is active would be in line with the behavior of other items.