kutty-bootstrap: Abstraction for color combinations

[nikochiko]

There could be different color combinations for a container element in which we can customize the border, background and text colors. This is the case for mutiple elements such as alert, card, button, and maybe even table.

We should find a consistent way to apply these customizations.

[nikochiko]

Here we need to set whether we want to be opinionated (group combinations together into fixed styles) or allow tweaking each dimension individually.

It can be styled with a background color and text color (fill style), or with a border color and text color (outline style). That would be high level but also inflexible in that it'll be harder to mix and match.