What are these black keys doing in C major?

Explaining the term "non-diatonic" and looking at some common sources of non-diatonicism in popular music.
Major scale guide: www.pianofluency.com/majorscales
Courses and free resources: pianofluency.com/
Lessons: calendly.com/tedcasemusic/int...
0:00 intro
0:56 what is "non-diatonic?"
2:50 a favorite example from Richard Rodgers
4:31 secondary dominants
9:37 borrowed chords
14:05 wrapping up