Can not minify the css code with webpack

Use OptimizeCSSAssetsPlugin to minify css assets, extractors are used to separate output assets only. Note that minification works with production mode i.e. make sure to pass "--mode production" in the webpack build command.

    {....,
        optimization: {
                minimizer: [
                   //Incase you want to uglify/minify js
                    new UglifyJsPlugin({
                        cache: true,
                        parallel: true,
                        sourceMap: true
                    }),
                    new OptimizeCSSAssetsPlugin({
                        cssProcessorOptions: { discardComments: { removeAll: true } },
                        canPrint: true
                    })
                ]
         }
    ....}

With webpack version above 4 you may like to use mini-css-extract-plugin instead of ExtractTextPlugin plugin