MDC Dark Theme + Toggle Roadblock

[HopperMCS]

As stated in #25, usage of the built-in "dark theme" has been requested. I don't know a soul who doesn't switch Twitter to dark mode, and Discord is another example.

We may need a separate JS file to do this for us. I would recommend modding the DOM through JS instead of modding the HTML for this, and we need to figure out which components need it and which keep the primary / secondary colors.

Creating as a separate issue because we have other stuff to tend to.