org-sourcehut is a theme for org mode's HTML export. It is intended to look like sourcehut's wiki service. It uses the original CSS file from the site, but runs a javascript program to change the format of what org mode outputs into something similar to sourcehut's HTML.
You can add this to the top of your org-mode file to use the theme without downloading anything:
#+SETUPFILE: https://demenses.net/org-sourcehut/sourcehut-remote.setup
Or, you can clone this repo to your org directory and use this to only use local files:
#+SETUPFILE: org-sourcehut/sourcehut.setup
Either way, once you've got one of these in your org file, just export to HTML as normal, and it should look nice.
Obviously the original CSS belongs to Drew Devault, and the setupfile-based theme structure is from org-html-themes.