Improve portability to vitejs or other bundler by cleaning the code

[Angra974]

react-play is build with cra.
CRA implementation make it works in the certain way that can't be often handle by another builder.
Some steps can be taken to be able to use the application with CRA and other bundler to make the process more smooth.

For exemple,
we import "index.css" directly in index.jsx file but the correct way is to import it relatively with "./index.css".
It didn't set a warning with CRA as it is an expected behavior but the code is not clean and make migration more difficult.

Here will be an attemps to smooth this transition by adding some little change without breaking the actual code.

[github-actions]

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