[css-color-6] Make color-contrast() candidates optional #7345
Description
From https://www.w3.org/TR/css-color-5/#winner
If there is a target contrast, and the end of the list is reached without meeting that target, either white or black is returned, whichever has the higher contrast.
However, a lot of the time getting either black or white is exactly what you want. If this is the default behavior, people shouldn't have to do dummy things like color-contrast(var(--color) vs white, black) or even color-contrast(var(--color) vs var(--color), var(--color)) etc, they should just be able to do something like color-contrast(var(--color)) and get either white or black.
I.e. change the grammar from:
color-contrast() = color-contrast( <color> vs <color>#{2,} [ to [<number> | AA | AA-large | AAA | AAA-large]]? )
to:
color-contrast() = color-contrast( <color> [ vs <color>#{2,} [ to [<number> | AA | AA-large | AAA | AAA-large]]? ]? )