When I first started experimenting with SASS, the first thing I did was look for a VS Code plug-in to add SASS automatically to my project; nevertheless, when I started working with other people that had different code editors, this became an issue.
I took the time to check some YouTube videos and found a quick way to add SASS to your React project, no matter in which state the project is.
I'm not going to make this as those people who create food recipes that tell their life story before posting the actual information, so...
Create your React project
Open your terminal of choice and input:
npm install --save-dev node-sass
Create a folder called Styles inside your
Inside the Styles folder create a variables.scss sheet.
Convert App.css to App.scss and move it inside Styles
Go to App.js and change App.css to App.scss. It should be at the top, on your imports.
Go to App.scss and import your variables sheet (variables.scss)
If you are lazy or just in a hurry, I created a downloadable repo with all of the above already implemented.