Our video player needed redoing (it was videogular before, we're using Vue now).
For the seek/progress bar, I thought I'd use <input type="range" min="0" :max="player.duration">
which is nice and straightforward because there's no JS to really write for it, and because it's a browser built-in widget, it's accessible as heck.
One problem: IE is the only browser that lets you style the background colour of the slider track differently according to whether it's before or after the current slider position (it's call the "thumb" for some reason).
Solution: CSS custom properties, linear-gradient background. Use JS to update the custom property when the video time changes: