I've built a CSS completions file which is available on my GitHub. I hope that they are much more useful than the default Snippets as you can supply property values just by typing one or two letters. (It's only for properties/values, not for selectors.)
I use camelCase, such as borderBottomStyle, to distinguish my completions. I then type 'borBS' to use it.
I haven't included poorly supported, animation, or browser-specific properties. Eventually you might consider moving the default snippet folders out of Packages\CSS, although there are some in the Other folder that I haven't replaced.
PS I mentioned this in 'Plugin Development' but it was suggested that this area is more suitable.