Package ruby-compass is not available for Ubuntu 20.04 LTS
While running:
docker build -t registry.labs.nic.cz/turris/foris/foris-demo .
I got error that ruby-compass is not available and I could find that in Ubuntu repository https://packages.ubuntu.com/bionic/ruby-compass it was present in Xenial 16.04 LTS and Bionic 18.04 LTS, so newer version LTS does not have it.