You are free to clone the repo and make any changes to the application code that you want, adding your own customization and features. After that you can build a docker image by running yarn build:docker or alternatively run docker build and pass your own args that is necessary.
For running app container from freshly built image do
docker run -p 3000:3000 --env-file <path-to-your-env-file> <your-image-tag>Disclaimer Do no try to generate production build of the app on your local machine (outside the docker). The app will not work as you would expect.