The goal is to revamp CMB2 css to allow theming/skinning to be more easily accomplished. The nested selectors creates difficulty. Once the CSS is not as nested, it will be easier (hopefully) to make the styles cleaner/better/faster/stronger, and to get snazzy.

Of crucial importance when contributing to this milestone:
CMB2 needs to provide full backwards-compatibility. While we are 100% on-board with improving the UI, we cannot break something for the 100s of thousands of users. Ideally, user-testing should be involved.