My browser somehow compliles .scss files from my React App without any .css file

I present you this scenario:

1. I have a React App.
2. I want to use node-sass
3. I install the package
4. I watched a youtube tutorial about sass integration with react.js
5. I followed the exact instructions (Rename all my .css file to .scss and change all the imports)
6. I wrote some scss and It's working just fine.

BUT I HAVE NO .CSS FILE TO COMPLILE MY .SCSS and it's working. So is this ok? I just rename all my files and start writing scss and it seems like the browser is compiling scss.

Am I doing something wrong?