title: CSS styling is missing for Vue.js packages
body: <p>I'm using a Vue.js WordPress starter plugin. (<a href="https://github.com/tareq1988/vue-wp-starter" rel="nofollow noreferrer">https://github.com/tareq1988/vue-wp-starter</a>) In general its a basic Vue installation with some toolbelts.</p>
  <p>The Vue app works fine. But when I try to install additional packages, for example UI frameworks like <code>Buefy</code>, the CSS styles for the different UI components are not showing. I tried it with different packages. Always the same result. No error messages, but the CSS is missing.</p>
  <p>How I embed the package:</p>
  <pre><code>import Buefy from 'buefy'
  import 'buefy/dist/buefy.css'
  Vue.use(Buefy)
  new Vue({
    el: '#vue-admin-app',
    router,
    render: h =&gt; h(App)
  });
  </code></pre>
  <p>Easy...</p>
  <p>I think that could has anything to do with the <code>mini-css-extract-plugin</code> for WebPack. Is this possible? Here I tried many versions, but none of these worked.</p>
  <p>This is the Webpack configuration:</p>
  <pre><code>const webpack = require('webpack');
  const path = require('path');
  const package = require('./package.json');
  const VueLoaderPlugin = require('vue-loader/lib/plugin');
  const HtmlWebpackPlugin = require('html-webpack-plugin');
  const BrowserSyncPlugin = require('browser-sync-webpack-plugin');
  const TerserJSPlugin = require('terser-webpack-plugin');
  const MiniCssExtractPlugin = require('mini-css-extract-plugin');
  const OptimizeCSSAssetsPlugin = require('optimize-css-assets-webpack-plugin');
  const config = require( './config.json' );
  
  const devMode = process.env.NODE_ENV !== 'production';
  
  // Naming and path settings
  var appName = 'app';
  var entryPoint = {
    frontend: './src/frontend/main.js',
    admin: './src/admin/main.js',
    style: './assets/less/style.less',
  };
  
  var exportPath = path.resolve(__dirname, './assets/js');
  
  // Enviroment flag
  var plugins = [];
  
  // extract css into its own file
  plugins.push(new MiniCssExtractPlugin({
    filename: '../css/[name].css',
    ignoreOrder: false, // Enable to remove warnings about conflicting order
  }));
  
  // enable live reload with browser-sync
  // set your WordPress site URL in config.json
  // file and uncomment the snippet below.
  // --------------------------------------
  // plugins.push(new BrowserSyncPlugin( {
  //   proxy: {
  //     target: config.proxyURL
  //   },
  //   files: [
  //     '**/*.php'
  //   ],
  //   cors: true,
  //   reloadDelay: 0
  // } ));
  
  plugins.push(new VueLoaderPlugin());
  
  // Differ settings based on production flag
  if ( devMode ) {
    appName = '[name].js';
  } else {
    appName = '[name].min.js';
  }
  
  module.exports = {
    entry: entryPoint,
    mode: devMode ? 'development' : 'production',
    output: {
      path: exportPath,
      filename: appName,
    },
  
    resolve: {
      alias: {
        'vue$': 'vue/dist/vue.esm.js',
        '@': path.resolve('./src/'),
        'frontend': path.resolve('./src/frontend/'),
        'admin': path.resolve('./src/admin/'),
      },
      modules: [
        path.resolve('./node_modules'),
        path.resolve(path.join(__dirname, 'src/')),
      ]
    },
  
    optimization: {
      runtimeChunk: 'single',
      splitChunks: {
        cacheGroups: {
          vendor: {
            test: /[\\\/]node_modules[\\\/]/,
            name: 'vendors',
            chunks: 'all'
          }
        }
      },
      minimizer: [new TerserJSPlugin({}), new OptimizeCSSAssetsPlugin({})],
    },
  
    plugins,
  
    module: {
      rules: [
        {
          test: /\.vue$/,
          loader: 'vue-loader'
        },
        {
          test: /\.js$/,
          use: 'babel-loader',
          exclude: /node_modules/
        },
        {
          test: /\.less$/,
          use: [
            'vue-style-loader',
            'css-loader',
            'less-loader'
          ]
        },
        {
          test: /\.png$/,
          use: [
            {
              loader: 'url-loader',
              options: {
                mimetype: 'image/png'
              }
            }
          ]
        },
        {
          test: /\.svg$/,
          use: 'file-loader'
        },
        {
          test: /\.css$/,
          sideEffects: true,
          use: [
            {
              loader: MiniCssExtractPlugin.loader,
              options: {
                publicPath: (resourcePath, context) =&gt; {
                  return path.relative(path.dirname(resourcePath), context) + '/';
                },
                hmr: process.env.NODE_ENV === 'development',
              },
            },
            'css-loader',
          ],
        },
      ]
    },
  }
  </code></pre>
  <p>Do you have an idea?</p>