shabitica VS NixOS-docker

I found [this software, shabitica}(https://github.com/headcounter/shabitica) that supposedly runs under nix. How do I get this to run in a nix docker container? That is run this all from within a docker container, not docker on nix.

It's open source: https://github.com/HabitRPG/habitica There's a fork meant for self hosting with stuff like monetization taken out: https://github.com/headcounter/shabitica

Something like Habitica? https://github.com/headcounter/shabitica

Luckily, I did not have to start from scratch as Nix serves their own docker image. I mounted one of my directories and was able to drop into a Nix shell with my configuration file.

There is one: https://github.com/NixOS/docker

But it's more of a Nix docker image than a NixOS one, because half of the things that NixOS gives you don't really make much sense in a docker image (systemd in a container?).

I only know of the nix package manager. https://hub.docker.com/r/nixos/nix

Ability to run buildkite agents inside a kubernetes cluster on preemble instances without need to modify agent’s Dockerfile every time new dependency comes up - was one of major reasons to learn Nix. I’m just using nixos/docker image as a base, install buildkite-agent and some base stuff like bash via nix-env inside Dickerfile, everything else lays in flake.nix of every project my dockerized nixified buildkite agent run.