configure sass with webpack for react code example

Example 1: node sass version react

yarn add [email protected]

Example 2: how to use sass in react without eject

#### Using sass in react without ejecting
#1.First install node-sass
npm i --save-dev node-sass

#2.Then install npm-run-all
npm install --save npm-run-all

#Then change the scripts of package.json:

#  "scripts": {
#    "build-css": "node-sass src -o src",
#    "watch-css": "npm run build-css && node-sass src -o src --watch --recursive",
#    "start-js": "react-scripts start",
#    "start": "npm-run-all -p watch-css start-js",
#    "build": "npm run build-css && react-scripts build",
#    "test": "react-scripts test --env=jsdom",
#    "eject": "react-scripts eject"
#  }

#After that, create a scss file beside each css file with the same name
#then run:
npm start

#after that every time you change the scss files, css files also ill be updated.
# !!! no need to change the imports of css files