We have a gallery of examples on our website, Discourse customers | Discourse - Civilized Discussion
The #theme category has all the themes, full themes are tagged #theme-full and theme components are tagged #theme-component. There’s also a category for #plugins.
We have theme documentation under #howto:devs with the #themes tag (maybe this tag should be named in a way that makes its use clearer outside of that category).
Are you looking for a gallery where you can see what themes and theme components look like without entering a topic? That’s potentially a customization we can add to our theme category at some point, and maybe an intro banner that explains what I just listed above.
What needs to be referenced? this is a user that was sharing what they were experimenting with on their own site, you’d need to ask them to share their CSS if that’s what you’re after. Same with Sharing our experience changing the Discourse UI.
What specifically would help you? Are you looking for more specific documentation on how to theme certain aspects of Discourse? For example, a guide on modifying the layout of the topic list? General component-specific theme guides are something I’ve been wanting to do.
Do you have an example of another site/platform that does what you’re looking for well? Appreciate the feedback, we definitely want to make things easy to find!