These hostnames were one of the most confusing part of the setup. You have nginx, which is looking for the 0.0.0.0, which doesn't work with the example docker because it uses docker networking, so you have to use the docker hostnames. Which is great, but then you have to tell nginx to not use the system dns resolver but docker's.
Then, you have environment variables everywhere for "host" which I personally had no idea if they mean the host (docker container), the host (actual machine localhost), or the host (full domain.tld)