The short answer is: It doesn't matter. Use whichever style you prefer, just try to be consistent.
The long answer is:
People have been asking this kind of question since CSS became a thing. There are all kinds of answers out there that will argue one way or the other, citing performance implications or maintainability.
None of that matters because:
- Browsers are so efficient that any performance difference is completely moot.
- Worrying about optimizing your inclusion paths is a distraction, and you're better off just writing code.