index.js

import css from "./styles.css";
function fn() {
  return css.foo;
}
console.log(fn);

main.js (no boilerplate)

function(e,r,t){"use strict";t.r(r);var n="_3TUThIrRsBDXr654gzsxg5";console.log((function(){return n}))}

styles.css

.foo {color: red}
.bar {color: blue}

webpack.config.js

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

module.exports = {
  devtool: false,
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: MiniCSSExtractPlugin.loader,
            options: {
              esModule: true
            }
          },
          {
            loader: "css-loader",
            options: {
              modules: true,
              esModule: true
            }
          }
        ]
      }
    ]
  },
  plugins: [new MiniCSSExtractPlugin({})]
};