oc(style): ui refinements?

[bdarcus]

Current state of style editing UI for org-cite:

So I'm using two faces to distinguish different parts.

1. highlight, here only applied to the styles without variants
2. the default face for the rest

These are same two faces used in the browsing UI.

Questions:

1. should the highlight face also apply to the preview?
2. should I add a face for mid-level hierarchy, and apply that here?