Border Color

Minor CSS optimization for border and border color.

For the border itself, we don't need to include the color in ```border: {}```, color is already added in ```border-color: {}```. 

Since the Theme uses shorthands for padding/margins, why not do the same for the border colors as well.
Merge pull request #500 from emiluzelac/patch-22

Simplifies `border-color` attributes.