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:

https://www.gstatic.com/youtube/img/originals/ckee/[email protected]

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: