Which CSS selectors or rules can significantly affect front-end layout / rendering performance in the real world?

Question

Is it worth worrying about CSS rendering performance? Or should we just not worry about efficiency at all with CSS and just focus on writing elegant or main

Answer 1

While not directly code-related, using over @import to include your stylesheets provides much faster performance.

'Don’t use @import' via stevesouders.com

The article contains numerous speed test examples between each type as well as including one type with another (ex: A CSS file called via also contains @import to another css file).