Is there a :not() pseudo class available (see here)? If not, are there any plans to support this and when can we reasonably expect this part of CSS to be available in the new UI system? 
This pseudo class is not supported and as far as I can see, no support for it has been planned.
+1 for :not() support or inherit
I have a simple use case that I cannot find a way to achieve otherwise:
I want to modify a style of an element but not if it is in focus.
another +1 for :not()