You should take a look to our #theme category and see how other Discourse sites have been customized.
For example
- https://discuss.newrelic.com/
- https://community.unbounce.com/
- https://forum.tudiabetes.org/
- https://experts.feverbee.com/
- https://ideas.weloveideas.com/
- https://community.revolut.com/
- https://www.secopshub.com/
- https://discuss.codecademy.com/
- https://forums.episodeinteractive.com/
- https://forums.docker.com/
- Forum - Banjo Ben Clark
- https://realtimevfx.com/
- https://community.starlingbank.com/
- https://community.imgur.com/
- https://forums.gearboxsoftware.com/