Additional Prose refinements

[aaronshekey]

This PR refines some more spacing, most notably when headers are stacked against paragraphs.

This:

1. Gives documentation a new, nicer example of some of the choices that were made. Check the "Minimal" example.
2. Spreads headers out from paragraphs so they're grouped with the following paragraphs.
3. Tightens up paragraphs a bit, and made sure headers are consistent.
4. Replaces all margins internal to the component with a CSS variable so our users can more easily monkey with it in their browsers and userscripts.