I just want Sass

webpackfile.js

const webpack = require('webpack');
const path = require('path');
var customProperties = require("postcss-custom-properties");

var cssApply = require('postcss-apply');
var autoprefixer = require('autoprefixer');

module.exports = env => {
  if (!env) env = {}
  const addPlugin = (add, plugin) => add ? plugin : undefined;
  const ifProd = plugin => addPlugin(env.prod || false, plugin);
  const removeEmpty = array => array.filter(i => !!i);

  return {
    entry: './src/',
    output: {
      filename: 'ui-primitives.js',
      path: path.resolve(__dirname, 'dist'),
      pathinfo: !(env.prod || false),
      libraryTarget: 'commonjs2'
    },
    module: {
      loaders: [
        {
          test: /\.jsx?$/,
          exclude: /(node_modules|bower_components)/,
          loader: 'babel'
        },
        { test: /\.css$/, loader: 'style-loader!css-loader!postcss-loader' },
        { test: /\.png$/, loader: 'url-loader?limit=100000' },
        { test: /\.svg$/, loader: 'file-loader' },
      ],
    },
    plugins: removeEmpty([
      ifProd(new webpack.optimize.DedupePlugin()),
      ifProd(new webpack.LoaderOptionsPlugin({
          minimize: true,
          debug: false,
      })),
      ifProd(new webpack.DefinePlugin({
        'process.env': {
          NODE_ENV: '"production"',
        },
      })),
      ifProd(new webpack.optimize.UglifyJsPlugin({
        compress: {
          screw_ie8: true,
          warnings: false,
        },
      })),
    ]),
    postcss: function () {
      return [
      require('postcss-npm')(),
        customProperties({preserve: true}),
        cssApply,
        autoprefixer,
      ]
    },
  }
};