Expose styles via reagent atom in SCI

[sritchie]

I'd love to be able to wrap my Mafs and MathBox viewers in a div that sets their styles based on the Clerk style active at the moment.

It would be great to expose the current style (as a map of variable => value, maybe?) in a reagent atom that I can deref, so my component will change when the user toggles dark/light mode.