Correct, you don't need the :nots as long as the CSS is in that order, since the :after content would be overridden correctly. You would need them if you changed the order of the statements.
I started the experiment using background color instead of "fizz", border color instead of "buzz", and box-shadow instead of "fizzbuzz" which necessitated the need for :nots since the properties weren't overriding.
I started the experiment using background color instead of "fizz", border color instead of "buzz", and box-shadow instead of "fizzbuzz" which necessitated the need for :nots since the properties weren't overriding.