webpack.config.js

const path = require('path');
const OptimizeCSSAssetsPlugin = require('optimize-css-assets-webpack-plugin');

module.exports = {
  mode: process.env.NODE_ENV === 'production' ? 'production' : 'development',
  entry: ['./src/yellow/gaiden.scss', './src/default/gaiden.scss'],
  output: {
    path: path.resolve(__dirname, 'dist'),
  },
  resolve: {
    extensions: ['.js', '.scss']
  },
  optimization: {
    minimizer: [new OptimizeCSSAssetsPlugin({})],
  },
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: [
          {
            loader: 'file-loader',
            options: {
              name: '[name].css',
              outputPath: (url, resourcePath, context) => {
                if (/default/.test(resourcePath)) {
                  return `default/${url}`;
                }

                return `yellow/${url}`;
              }
            },
          },
          {
            loader: 'extract-loader'
          },
          {
            loader: 'css-loader?-url'
          },
          {
            loader: 'postcss-loader'
          },
          {
            loader: 'sass-loader'
          }
        ]
      },
    ]
  }
}