Presumably they can't just use one dash to avoid clashes with vendor prefixes (-moz-, -webkit- etc.)
I don't think I've ever actually checked, but I always assumed valid CSS property names can only be alpha-dash strings.
I don't think I've ever actually checked, but I always assumed valid CSS property names can only be alpha-dash strings.
They are, although they also aren't allowed to start with a number. But like most things on the web you're not supposed to do some browsers will still let you get away with it.