is what greeted me this morning.Doesn't seem to matter which theme I use.  So it is unlikely to  be a css problem; the theme it happened with last night was is as is, out of the box.What I'll probably do, then, is (a) keep researching to find the problem, which seems to be wordpress-wide, and (b) provide people with a Theme Switcher so that they can pick the theme they like.In time.