``` color-mix() = color-mix( <color-interpolation-method> , [ <color> && <percentage [0,100]>? ]#{2}) ``` ``` cross-fade() = cross-fade( <cf-image># ) <cf-image> = <percentage [0,100]>? && [ <image> | <color> ] ``` The `color-mix()` and `cross-fade()` functions have different grammar orders wrt progress and value, they should probably be synchronized.