Yep, finally got my new theme in working order. It looks good in Firefox, IE and Opera, and it even seems to work on a lower resolution screen (ie, without pushing the sidebar down to the bottom of the screen). But if you use another browser (or a Mac) and weird things are happening, please let me know.
It’s not exactly a radical change. I just fancied a slightly different colour scheme (I might tweak it a bit further). But it’s surprising how much work that can create when you’re as much of an amateur as I am. (This is very very loosely based on one called Dark Maple that I found here; I thought it was really pretty, but I didn’t want the whole package.)