Implement the Raising Dark Mode Functionality

[mlaursen]

The new dark theme specs are actually really nice and look much better than the current dark theme I implemented by default. The main problem with this is that I need to somehow link elevation and colors together and allow for conditionally switching between light and dark themes.

This issue is more just a reminder for myself to stop playing with implementing it for initial v2 release and it should be scoped for later. The two work-in-progress branches/commits are here:

• wip/dark-theme-elevation-1 e89ee6e
• wip/dark-theme-elevation-2 f05ec16

I think I want to go more towards v1 of these two due to the colors not using opacities in that version. The "blockers" for this are that I might need to handle some of this in JS instead of CSS only, force a specific dark theme class name/media query, or something else.