I'm pretty sure I already made this comment last year, but I don't think anything has changed.
While on dark mode, without any theme applied, the volume slider colours are not great, grey on less grey. The volume level colour should just be the accent colour (eg. Blue when no theme is applied). Same for the brightess level but that's easier to see with the always black background.
I think there's a good lock module (Theme Park IIRC) that fixes that but that's not the point.
However, as design-related suggestions can be highly subjective, their implementation depends on the number of users supporting such an idea. Generally speaking, the more users refer to your suggestion and more votes will be gathered under this post, e.g. in the form of likes from other users, the more likely the suggestion will be taken into consideration. 😊