Error: Cannot resolve module 'style-loader'

Please run this script:

 npm install style-loader css-loader --save

Set your module as below:

module: {
  loaders: [
    {
      test: /\.jsx?$/,
      loader: 'babel-loader',
      include: path.join(_dirname, 'app')
    },
    {
      test: /\.css$/,
      loader: 'style-loader!css-loader'
    }
  ],
  resolve: {
      extensions: ['', '.js', '.jsx', '.css']
  }
}

It's basically reading as for loaders - test jsx using babel-loader and the next test is a css file using style-loader and css-loader, which will recognize the modules. Also, you should exit out of npm start, and run "npm install" and run "npm start". Hopefully, this should take care of the issue.

Try run script below:

npm install style-loader --save

Modify webpack config, add modulesDirectories field in resolve.

    resolve: {
        extensions: ['', '.js', '.jsx', '.css'],
        modulesDirectories: [
          'node_modules'
        ]        
    }