The tools are Compass combined with Sass (which means Sytactically Awesome Stylesheets or some random crap like that).
Sass is cool because it lets you do a whole bunch of stuff with CSS that you couldn’t normally. It’s a kind of abstraction layer above CSS which means you can write normal CSS if you want, but then why wouldn’t you just write normal CSS instead of using Sass?
I’m getting slightly ahead of myself, but With Sass you can do awesome things like variable/placeholders which is awesome for things like defining core elements of a stylesheet such as a palette of colors.