I’m guessing this is from their Karate Kid thing a couple of years ago, but the YouTube CSS still includes references to a crane kick file:
To activate, you need to add a custom attribute of
ytp-scrubber-container to some parent of
.ytp-scrubber-container and then you’ll need to also manually turn off the opacity and transform. There’s a hover attribute this is supposed to do this but it is to a sibling item which won’t invoke with the selectors.
If you get it right, you’ll end up with: