Soundslice ( https://www.soundslice.com/ ) — a website built around interactive/responsive sheet music, rendering the music entirely in client-side JS — doesn't use JavaScript frameworks or libraries. I'm the developer of Soundslice and continue to be happy with the vanilla JS decision, 8+ years into the company. It means better performance, clearer code, smaller JS filesizes. I gave a talk about it here: https://www…
You are using fractional units to position it, but you're also using left/top/height properties which can't be fractional.
If you convert these to GPU translated layers via translate, you'll get a smoother playhead since these can be positioned fractionally, plus you'll cut down on the repaints!
Here's an example: https://codesandbox.io/s/magical-wind-mptqn?fontsize=14&hide...