unofficial extensions? haven't heard of those yet. Currently I'm quite simply horrified by the utter inadequacy of CSS3 doing the job that people do with it. Now granted, it wasn't exactly designed to do that job originally, but it was foreseeable. And at least now we really should make something new that is designed from scratch to be a remote GUI framework and not eyecandy on content declarations...
CSS is definitely a nightmare for laying out designs. However, there are some tools that can help you. I use
LESS for writing my code. It enables variables, mixins (pseudo-functions) and nested rules (e.g. defining the hover of a link directly into the "a" definition) just to name a few.
In order to ensure compatibility, I use
LessHat. It defines mixins so you can use "advanced" features on almost every web browser, without changing your syntax. My websites are all compatible with IE9 and higher, and usually can be browsed on IE8. And it doesn't rely on evil magic that makes your page 10 times slower. It simply adds the browser prefixes (e.g. -webkit, -ms, -opera, etc.) before the instructions.
Finally, for the layout, I use a file that I made from a post on StackOverflow. It defines responsive columns (like Bootstrap) directly in LESS. It's small and convenient.
I compile everything in a single CSS using
NodeJS and
Gulp and it makes effective CSS that is relatively easy to write.
However, CSS with or without LESS will stay unfriendly as hell. It takes time to get used to it.