Bonsai’s ‘sticky’ tabs…??

I’ve gotten most of the way toward mimicking Binary Bonsai’s horizontal tabbed navigation, but the one thing I can’t quite discern is whether he’s using Javascript (or Flash?) to ‘stick’ the tab-color once a selection has been made. Currently, mine just revert to the initial background-color, after selecting. That’s normal behavior I suppose, but I’d love the rollover-color to stick after selecting instead!

Hopefully I’m just missing a CSS attribute of some sort?

Cheers!