Please use https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#adding-a-css-preprocessor-sass-less-etc instead.
Enhances create-react-app to include support for Sass.
npm install create-react-app-sass --save-dev
Replace your start and build scripts in your package.json
"scripts": {
"start": "react-scripts-with-sass start",
"build": "react-scripts-with-sass build",
"test": "react-scripts test --env=jsdom",
"eject": "react-scripts eject"
},
Your src directory will automatically re-compile any .scss file into a .css file with the same name in the same location. Then you can import the .css file in your components the same way as before using create-react-app. You will also need to add *.css to your .gitignore file as they are now just a build artifact and your .scss is the true source.