Plone site in docker container

After I managed to install plone 6 from its packages I also wanted to try the variant with docker. The image for the backend was done quickly and the installation of the pas.plugins.ldap was also problem-free.
For the frontend I first had to find a Dockerfile to add the addons there. So far so good. But now the question arises as to how I can get my own files under theme and src or how these can be found by the Plone in the Docker image. My idea of embedding them via volumes doesn't seem to work.

- ./frontend/src:/app/src
- ./frontend/theme:/app/theme

I see the files in the running container in the right path for example under src/customizations/components/theme/Logo/Logo.svg

What am I missing here?