--hover variants of color surface 3 and 4

[TarkusLee]

--color-surface-2 has a hover variant, --color-surface-2--hover. It would be nice to have these variants for each surface color.

[alistair3149]

Putting this on hold for now because I am hesitated to introduce new colors since they are due to a rework after MW 1.43 drops, which is around the end of the year.

In the meantime, you can add these to your MediaWiki:Citizen.css:

:root {
	/* Add extra hover and active state colors */
	--color-surface-3--hover: hsl( var( --color-primary__h ), var( --color-surface-3__s ), calc( var( --color-surface-3__l ) + var( --delta-lightness-hover-state ) ) );
	--color-surface-3--active: hsl( var( --color-primary__h ), var( --color-surface-3__s ), calc( var( --color-surface-3__l ) - var( --delta-lightness-hover-state ) ) );
	--color-surface-4--hover: hsl( var( --color-primary__h ), var( --color-surface-4__s ), calc( var( --color-surface-4__l ) + var( --delta-lightness-hover-state ) ) );
	--color-surface-4--active: hsl( var( --color-primary__h ), var( --color-surface-4__s ), calc( var( --color-surface-4__l ) - var( --delta-lightness-hover-state ) ) );
}