What do the red rectangles on the timeline mean?

Question

Adobe After Effects

Hello, I’m just learning AF and I can’t understand so far only one thing, why is it highlighted in red for me
How to remove it and what is it all about?
Appeared after I opened Sequence Settings and immediately closed it, what could be the reason?
Initially, the maximum number of frames on TimeLine was 30 (for example, 00:00:09:30), but after opening and closing the sequence settings, 60 frames appeared (as it should be on the project) and after that it was already 00:00:09:60 and red rectangles appear

Answer 1

Shifting the sound relative to the video sequence.
And you comprehend ae being in the premiere? Interesting.