Minimal CSS Modules + PostCSS webpack config

postcss.config.js

module.exports = {
  plugins: {
    'postcss-cssnext': {},
    // other plugins (https://github.com/postcss/postcss#plugins)
    'cssnano': {}
  }
}

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              importLoaders: 1,
              modules: true
            }
          },
          'postcss-loader'
        ]
      }
    ]
  }
}