To be investigated, this is the only device I could test it on at the moment.

At the moment, the background of the slider selector is transparent.
This should be the case when it is not expanded, but it needs a solid background when it is expanded.
I was thinking of having it cover the whole page eventually, and be easily scrollable.
When working on this issue, if not enough sliders are existent, add more items to the sliders array for testing purposes and push the branch with the sliders in order for the reviewers to easily test it. They should be removed after one reviewer comments that all of the features work correctly.

I'm open to more design suggestions, the only requirements are that the selector should be scrollable in order to permit the addition of (theoretically) unlimited sliders while being easily usable.

I also want to keep the same view for desktop and mobile, so I expect the menu to be usable on both.

It would be nice if the slider selector had a smooth transition, with a transition: .3s; property to match all the UI elements.
The transition should be valid and work even when more items are added to the slider list.

As per the comments near referenced line, audio volume is not adjustable in iOS Safari. I was not able to find a fix for this, needs to be investigated.