Add CSS variable support for card colors

[GeorgeNance]

This will allow us to change the default card colors without needing to recompile

[FairyPenguin]

hey,
is this still open?

Can I start contributing?

[melloware]

Sure thing I am pretty sure I can merge PR's

[FairyPenguin]

Sure thing I am pretty sure I can merge PR's

Thanks, I hope I get this right, what is required [creating color variables in the scss file] or in separate colors.scss file depending on the current colors right?