Webpack 4 config.js (Postcss and Babel) 👌 The Simplest Usage 👌

package.json

{
  "name": "webpack-postcss,
  "version": "1.0.0",
  "scripts": {
    "start": "webpack-dev-server --open --mode development",
    "build": "webpack -p"
  },
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.4",
    "babel-preset-es2015": "^6.24.1",
    "css-loader": "^0.28.11",
    "postcss-cssnext": "^3.1.0",
    "postcss-loader": "^2.1.3",
    "style-loader": "^0.20.3",
    "webpack": "^4.5.0",
    "webpack-cli": "^2.0.14",
    "webpack-dev-server": "^3.1.1"
  }
}

postcss.config.js

module.exports = {
  plugins: {
	'postcss-cssnext' : {}
  }
}

webpack.config.js

/* === dont forget to import css to main.js file === */
/* ===> import './main.css'; <=== */


var path = require("path");

module.exports = {
  entry: "./main.js",
  output: {
    path: path.resolve(__dirname, "dist"),
    filename: "bundle.js",
    publicPath: "/dist"
  },
  module: {
    rules: [
      {
        test: /\.js$/,
        use: {
          loader: "babel-loader",
          options: { presets: ["es2015"] }
        }
      },
      {
        test: /\.css$/,
        use: [
          {
            loader: "style-loader" // creates style nodes from JS strings
          },
          {
            loader: "css-loader" // translates CSS into CommonJS
          },
          {
            loader: "postcss-loader" // compiles Postcss to CSS
          }
        ]
      }
    ]
  }
};