Conditional CSS
I've been writing CSS for well over a decade, and as much as I love it, there's one thing I've always been irked about. The language lacks an explicit if/else syntax because the authors felt that the presentation layer shouldn't be responsible for "behavior", which is how they think of logic. So what's funny here is that this article perfectly illustrates why the lack of an else/if is just pure silliness. There's "behavior" embedded everywhere in CSS, it's just all so implicit that it almost goes unnoticed.