v4: light vs dark in navbars and cards

Created by: bassjobsen

I found that the navbar component uses the navbar-light, navbar-dark classes to create link colors. The output of this classes can be set with the $navbar-light- and $navbar-dark-* variables. The card modules uses a .card-inverse to set a light font. Should it be more consequent when the card module also got a card-light and card-dark class? Including some variable to set them?

Also the navbar use the contextual backgrounds classes, shouldn't the card modules use these classes too? Which requires having contextual border classes too.