webpack.config.js

module.exports = {
   module: {
      rules: [
         {
            test: /\.s[ac]ss$/i,
            use: [
               // Creates `style` nodes from JS strings
               'style-loader',
               // Translates CSS into CommonJS
               'css-loader',
               // Compiles Sass to CSS
               'sass-loader'
            ]
         }
      ]
   }
};