This video is now outdated. Not to worry! Here is a link to a section of Russ’s most recent course which covers the negation or not pseudo-class:
Russ Weakley is a world-renowned author, speaker and CSS expert, with a detailed knowledge of web design and development. Russ chairs the Web Standards Group (WSG) and produced a series of widely acclaimed Learnable tutorials on CSS. He is currently touring a series of Responsive Web Design workshops around Australia.