Might be nice to give this instance more Solarpunk like colors. I am currently a bit short on time to work on this myself, but contributions are welcome.

A nice banner image would be cool as well.

The documentation on theming is not very detailed, but it seems to be mostly just Bootstrap 4: https://join-lemmy.org/docs/en/administration/theming.html (Edit: that docu might be outdated and it is actually Bootstrap 5 now)

An example for a instance with a custom theme is here: https://compuverse.uk/