I've been doing some small features in Identity in preparation for the GNOME 50 update (not much time for apps so I usually update them when a new GNOME releases).
This one is curious: a hover popup that shows exactly where the video will seek when you click on the bar. Looks simple, but unfortunately needed plenty of hacks since GTK doesn't currently expose some necessary API.
Note how the time always matches, including to the very left and very right of the time slider.