Comment by rusackas

You can style dashboards with CSS as much as you'd like, though there are some limitations (canvas/webGL elements). I wrote a whole blog post on it: https://preset.io/blog/customizing-superset-dashboards-with-...

If you want to style the whole application, you can fork the repo and go bananas. If you're looking for theming, there's more to be done yet on that front, and I wrote an article on that too: https://preset.io/blog/theming-superset-progress-update/