It's expected that you will use your own Dockerfile for production.
See nginx directory for configurations. These get loaded as a docker-compose volume.
Environment variables are loaded by docker-compose from mysql.env.development.
See php for PHP related configuration files, healthcheck, and entrypoint.
The php/development/conf.d/20-overrides.ini.development file is used a base config to populate the git ignored php/development/conf.d/20-overrides.ini. The latter is actually loaded by PHP. This is to allow for easily toggling xdebug on and off via the Makefile.
Environment variables are loaded by docker-compose from php.env.development.