I have a Gatsby project that uses Theme UI and Netlify CMS.
How can I style the Netlify CMS preview pane with my Theme UI styles?
Netlify CMS doesn't support CSS-in-JS libraries:
https://github.com/netlify/netlify-cms/issues/793
Unlike Styled Components, it doesn't seem possible to convince Emotion to inject its styles into the Netlify iframe, either. There does appear to be some support for injecting raw CSS into the preview iframe:
https://github.com/netlify/netlify-cms/pull/1162
But so far I can't seem to figure out how to make any of this work together on my own.