Fix various bugs in our Monobook stylesheet

* Toolbar was too tall
** The actions toolbar is nested in the main toolbar, so the rule
   increasing the font size by 25% for toolbars applied to it twice
* Font size in link suggestions was too big
** Remove 25% font size increase from overlays
** Add it back on the context (otherwise it's too small)
** But only on the main surface's context (otherwise contexts in dialogs are too big)
* Make highlights and context appear below, not above, toolbar menus
** z-index: 4 was too high for the overlay, because MenuToolGroup also has 4
** But the default of z-index: 1 is too low because it puts dialogs behind the surface
** z-index: 2 seems to work

Bug: 69949
Change-Id: I19da270abcdbe526ff213f0eb7d0859b48276930
Merge "Fix various bugs in our Monobook stylesheet"