Ghost/ghost/announcement-bar/scripts/build-combined.js

const rewire = require('rewire');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
const defaults = rewire('react-scripts/scripts/build.js');
let config = defaults.__get__('config');

config.optimization.splitChunks = {
    cacheGroups: {
        default: false
    }
};

config.optimization.runtimeChunk = false;

// JS: Save built file in `/umd`
config.output.filename = '../umd/announcement-bar.min.js';

// CSS: Remove MiniCssPlugin from list of plugins
config.plugins = config.plugins.filter(plugin => !(plugin instanceof MiniCssExtractPlugin));
// CSS: replaces all MiniCssExtractPlugin.loader with style-loader to embed CSS in JS
config.module.rules[1].oneOf = config.module.rules[1].oneOf.map((rule) => {
    if (!Object.prototype.hasOwnProperty.call(rule, 'use')) {
        return rule;
    }
    return Object.assign({}, rule, {
        use: rule.use.map(options => (/mini-css-extract-plugin/.test(options.loader)
            ? {loader: require.resolve('style-loader'), options: {}}
            : options))
    });
});