webpack.common.js

const path = require("path");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");

module.exports = {
    entry: {
        app: './src/index.js'
    },
    output: {
        // filename: "app.js",
        path: path.resolve(__dirname, 'public')
    },
    module: {
        rules: [
            {
                test: /\.css$/i,
                use: [
                    MiniCssExtractPlugin.loader,
                    'css-loader',
                    {
                        loader: 'postcss-loader',
                        options: {
                            postcssOptions: {
                                plugins: [
                                    [
                                        'postcss-preset-env',
                                        {
                                            // Options
                                        }
                                    ]
                                ]
                            }
                        }
                    }
                ]
            },
            {
                test: /\.m?js$/,
                exclude: /(node_modules|bower_components)/,
                use: {
                    loader: 'babel-loader',
                    options: {
                        presets: ['@babel/preset-env', '@babel/preset-react'],
                        plugins: ['@babel/plugin-transform-runtime']
                    }
                }
            }
        ]
    },
    plugins: [new MiniCssExtractPlugin()]
};