React 'yarn start_dev' env file branch sample example program

I'm looking for a basic sample project to know how to handle env branching in react.

[Submit results]
1. When you're done, post the result on your github and give me the link. (Please exclude node_modules folder)

2. The output must be executed with the yarn start command.


[Requirements]
1. It should work even if 'REACT_APP_' is not attached.
For example, after putting in a value in the form of 'COMPANY= google', I should be able to get the value in the form of 'process.env.COMPANY'. (Not in REACT_APP_COMPANY form, just saved in COMPANY form)

2. When executed with the "yarn start_dev" command, the value "COMPANY=A" is entered,
When executed with the "yarn start_production" command, the value "COMPANY=B" is entered.
(In other words, branch processing to look at different values depending on execution)

3. I use a library called dotenv.
If there are additional libraries that need to be installed, I will also install them.