Support relative color syntax in values#243

I use a framework to AVOID using static values. Please enhance CF to allow relative color syntax so the whole system can be modernized and more flexible. Example:

–color-primary: red;
–color-primary-light: oklch(from var(–color-primary) calc(l * 1.15) c h);
–color-primary-dark: oklch(from var(–color-primary) calc(l / 1.15) c h);