Fix btn-light's active state color

[tpg-gulshan]

Fixes #35258

Fixes #34123

[ffoodd]

Thanks for submitting this!
This is not the best way though, since you're making an exception were we try to have a generic behaviour.

I think we need to question the light color itself, since your issue relates more to the color being to close to white (thus lightening it has almost no effect).

[ffoodd]

Back to this, I'd say either we consider darkening our default light color (which would concern everything using it) or we consider using the button-variant() mixin with defined parameters, instead of simply using the color itself.

I'd recommend going for this, since we also have contrast issues with some of our outline buttons, that would benefit from a less generic way of building buttons variants — meaning probably to drop the very simple loop and declare at least some variants indepently. This is used in Boosted at least, even if we don't need that much specificity.

By doing so, we could get closer to what v4 looked like. Not quite sure yet of how the best values to use, but if you want to give it a shot it'd be really appreciated :)

[tpg-gulshan]

Thanks, @ffoodd for your observations on this.
I'll look into it again and spend some more time fixing it in a different and better way. I will also consider your idea to make it done.

[mdo]

Is this still something you want to iterate on @tpg-gulshan or should we take a crack at it?

[mdo]

Thinking about this in another way in #36168.