Consider using `:current` (+ `:past` & `:future`) instead of `:checked` for markers

[Schepp]

I find the use of the :checked pseudo class not to be the ideal choice for something that is not a checkbox or switch. Instead what we wanna mimick in CSS is HTML's aria-current-attribute. This is best done via the existing :current pseudo class, which is currently used for video VTTs and already offers a way to mark the active element in a sequential row of elements. For markers that are located before and after the active marker, we could then also use the closely related :past and :future pseudo classes.

[tabatkins]

I don't think I agree with trying to repurpose the temporal pseudo-classes like this. They already have a meaning, independent of what you're proposing, which means that theoretically both sets of meanings could apply and be extremely confusing.

I agree that using :checked isn't ideal. The naming isn't great for the intended meaning, and in theory it runs into the same issue as above, but in practice I think they don't actually overlap in applicability.

If we don't like :checked, we can just invent a new word. No reason to be spendthrift here.

[yisibl]

In Customizable Select Element, :checked is used to represent the checked value, and we should keep the API consistent here if there is no particular reason to do so.

openui/open-ui#827 (comment)