Of course, the absolute extreme of reusable classes would be if each class applied exactly one CSS rule. Then you could mix and match them in any possible way,

Of course, the absolute extreme of reusable classes would be if each class applied exactly one CSS rule. Then you could mix and match them in any possible way, at the cost of having 18 classes per element. But no one would do that. You don't need every possible combination because you want some consistent styles throughout your site. In Nicole's examples, she's getting pretty sophisticated effects, and I don't see her applying more than 3 classes to any element. (http://oocss.org/module.html http://oocss.org/module.html)