Sharing Docker images of local Ghost blog for collaboration

I am just hosting a static version of my ghost blog on GitHub pages ( I would like to create a docker image of my localhost ghost blog code where i use a custom theme ( dawn ) , other customised settings and create posts. I would like to dockerize this whole localhost ghost code , push it to a repo in my dockerHub so that my other collaborators can download the docker image do their post creations , create an updated docker image from the changes and push it back to dockerHub. Because of the sparse requirement in content creation (happening rarely) it does not make sense to host this docker image on server (or digital ocean, AWS lightSail etc.). It is good enough to make edits to the ghost blog locally and push the static site to GitHub Pages.

Difficulty/ challenges in dockerizing local Ghost:

1.) I am able to pull the latest ghost docker image , make the required changes (change theme, make posts and configure other settings in the dashboard). These settings also persist when i stop the docker container and restart/ run it. I am also able to build a new image from the updated container and push it to a repo in DockerHub.
2.) The trouble starts When some one pulls my custom docker image from dockerHub, The docker image fails to build as the custom theme (dawn) is lost and even if i use the default Casper theme , i don’t see my new posts also.
3.) I also Tried GitHub Repo but it had issues with some index.js file missing and other path structures changing , so Other than docker and GitHub, is there any other (free) way to collaborate on development of a ghost blog.

If my above idea / requirement is possible.
Could anyone kindly provide the correct steps with docker code to get this working?

Best Regards,