The only theme I can stand to use. Simple, clean, and colors that don't punish the eye for daring to look at the screen. Thanks to this add-on, I have launched into a search for one similar on Thunderbird to not avail.
If it would be possible to bring this to TB, I would enjoy it all the more. :)
Again, the epitome of what a theme should be. Solid, clean, minimalistic so you don't have your screen space taken up by junk.