Does SDL Tridion use any CSS preprocessors to generate its stylesheets?

I'm working on a GUI extension and I'd like to work with the CSS that's already provided. But it'd be easiest -- if the CSS comes from a CSS preprocessor -- to just have those pre-processed .less, .scss, .sass, or .styl files. 

So does Tridion use a preprocessor. And if so, is it possible to share those files?