[css-forms-1] Have 2 slider-fill pseudos?

[nt1m]

It would probably be beneficial to have ::slider-fill-upper and ::slider-fill-lower (names to be bikeshed) as @thebabydino describes here: #4410 (comment)

There's also the multi-range proposal in Open UI: https://open-ui.org/components/enhanced-range-input.explainer/ which might good to coordinate with.

[lukewarlow]

What would this look like for a switch control?

I'm guessing perhaps something like ::slider-fill-lower is full width and ::slider-fill-upper is 0 width when checked, and vice versa when unchecked?

For the range control itself this makes sense to me, the more granular we can be with pseudo elements the better as it will allow us to address a larger percentage of use cases.