style-loader.js

          {
            test: /\.css$/,
            ...
          },
          // Add the above block to below
          {
            test: /\.scss$/, // Change .css to .scss
            use: [
              require.resolve('style-loader'),
              {
                loader: require.resolve('css-loader'),
                options: {
                  importLoaders: 1,
                  modules: true, // Add this option 
                  localIdentName: '[name]__[local]__[hash:base64:5]' // Add this option
                },
              },
              {
                loader: require.resolve('postcss-loader'),
                options: {
                  // Necessary for external CSS imports to work
                  // https://github.com/facebookincubator/create-react-app/issues/2677
                  ident: 'postcss',
                  plugins: () => [
                    require('postcss-flexbugs-fixes'),
                    autoprefixer({
                      browsers: [
                        '>1%',
                        'last 4 versions',
                        'Firefox ESR',
                        'not ie < 9', // React doesn't support IE8 anyway
                      ],
                      flexbox: 'no-2009',
                    }),
                  ],
                },
              },
              // Add 'sass-loader' with includePaths
              { 
                loader: require.resolve('sass-loader'),
                options: {
                  includePaths: [path.styles]
                }
              }
            ],
          },