https://github.com/SLaks/Silon#implementation-details https://github.com/SLaks/Silon/blob/gh-pages/styles/_operato...
The actual declarations end up being nicely simple; see https://github.com/SLaks/Silon/blob/gh-pages/styles/_themed-...
The CSS is just a truth table, but the LESS (which is Turing-complete) actually contains all of the logic.