yarn add sass-loader node-sass

node_modules/react-scripts/config/webpack.config.js

  {
              test:/\.scss$/,
              loaders: ['style-loader', 'css-loader', 'sass-loader']
            },    

const WorkboxWebpackPlugin = require('workbox-webpack-plugin')
plugins: [
        new MiniCssExtractPlugin({
            filename: '[name].css'
        }),
        new WorkboxWebpackPlugin.GenerateSW({
            clientsClaim:true,
            skipWaITing:true
        })
    ],