Use mixin to generate card color variations
Created by: bassjobsen
i found that in the current version the cards module has not got card-variant()
mixins, just like the button module.
Compare:
https://github.com/twbs/bootstrap/blob/v4-dev/scss/_card.scss#L90
and
https://github.com/twbs/bootstrap/blob/v4-dev/scss/_buttons.scss#L56
Of course i understand the card variant only set two properties, but on the other hand not having these mixins seems inconsequent and not futur proof?