I updated my installation to v2.2.1 and the theme works using my CONFIG.md linked above.
./silverbullet version
2.2.1-unknown
If you are open to recommendations, I would start with launching sivlerbullet to a new directory without anything, files or plugins, then test the theme. You may have already tried this approach. Using your browser’s private or incognito mode is great to avoid confusing browser caching issues. If it still doesn’t work, a more extreme approach is to move testing to a virtual machine, container (LXC or docker), or another computer and a clean install. I assume you are not using an apache, nginx, or caddy reverse proxy, but if you are, don’t, while testing. Fewer components to troubleshoot.
I have not explored silverbullet’s debug capabilities, but hopefully a clean environment will work so you can pinpoint the problem.
