config-overrides.js

const {
  override,
  overrideDevServer,
  addWebpackPlugin
} = require("customize-cra");
const CopyPlugin = require('copy-webpack-plugin');
const RewireMultipleEntry = require('react-app-rewire-multiple-entry');

const multipleEntry = RewireMultipleEntry([
  {
    entry: 'src/popup/index.js',
    template: 'public/popup.html',
    outPath: '/popup.html'
  },
  {
    entry: 'src/page/index.jsx',
    template: 'public/index.html',
    outPath: '/index.html'
  }
]);

const devServerConfig = () => config => {
  return {
    ...config,
    writeToDisk: true
  }
}

const copyPlugin = new CopyPlugin({
  patterns: [
    { from: 'public', to: '' },
  ]
})

module.exports = {
  webpack: override(
    addWebpackPlugin(
      copyPlugin
    ),
    multipleEntry.addMultiEntry,
  ),
  devServer: overrideDevServer(
    devServerConfig()
  ),
};