Port problem

Whilst the current image on Docker Hub works, if I rebuild from source, I have a problem with ports.

It seems some templating code sets the path to the CSS file for the theme including the hostname and port. This breaks when mapped to a different port on the host e.g. `-p 8000:1948`. The workaround is to do `-p 1948:1948`. This will still break if running on a VM not mapped to localhost.

Reproduce the problem by rebuilding the Docker image and running it with `-p 8000:1948`, then inspect the templating code that assembles the theme CSS path. Done means the CSS loads correctly when the container port is mapped to a different host port or accessed through a VM.

Written by the indexing model from the issue text.