Use css from cdn.kde.org

AetherTemplate.php

 <?php
+
+
 /**
  * Neverland - Modern version of MonoBook with fresh look and many usability
  * improvements.

JsonManifestNetworkStrategy.php

+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Symfony\Component\Asset\VersionStrategy\VersionStrategyInterface;
+
+/**
+ * Reads the versioned path of an asset from a JSON manifest file.
+ *
+ * For example, the manifest file might look like this:
+ *     {
+ *         "main.js": "main.abc123.js",
+ *         "css/styles.css": "css/styles.555abc.css"
+ *     }
+ *
+ * You could then ask for the version of "main.js" or "css/styles.css".
+ */
+class JsonManifestNetworkVersionStrategy implements VersionStrategyInterface
+{
+    private $manifestPath;
+    private $manifestData;
+
+    /**
+     * @param string $manifestPath Absolute path to the manifest file
+     */
+    public function __construct(string $manifestPath)
+    {
+        $this->manifestPath = $manifestPath;
+    }
+
+    /**
+     * With a manifest, we don't really know or care about what
+     * the version is. Instead, this returns the path to the
+     * versioned file.
+     */
+    public function getVersion($path)
+    {
+        return $this->applyVersion($path);
+    }
+
+    public function applyVersion($path)
+    {
+        return $this->getManifestPath($path) ?: $path;
+    }
+
+    private function getManifestPath($path)
+    {
+        if (null === $this->manifestData) {
+            $fileContent = file_get_contents($this->manifestPath);
+            if (!$fileContent) {
+                throw new \RuntimeException(sprintf('Error parsing loading manifest file "%s"', $this->manifestPath));
+            }
+            $this->manifestData = json_decode($fileContent, true);
+            if (0 < json_last_error()) {
+                throw new \RuntimeException(sprintf('Error parsing JSON from asset manifest file "%s" - %s', $this->manifestPath, json_last_error_msg()));
+            }
+        }
+
+        return isset($this->manifestData[$path]) ? $this->manifestData[$path] : null;
+    }
+}
+

SkinAether.php

 <?php
 /**
- * Neverland - Modern version of MonoBook with fresh look and many usability
- * improvements.
- *
+ * Aether
+
  * @todo document
  * @file
  * @ingroup Skins
  */
 
+require_once __DIR__.'/vendor/autoload.php';
+require_once 'JsonManifestNetworkStrategy.php';
+
+use Symfony\Component\Asset\UrlPackage;
 
 /**
  * SkinTemplate class for Neverland skin
@@ -46,8 +49,13 @@ class SkinAether extends SkinTemplate {
      * @param $out OutputPage object
      */
     function setupSkinUserCss( OutputPage $out ){
-        $out->addStyle( 'https://cdn.kde.org/aether/css/bootstrap.min.css', 'all' );
-        $out->addStyle(  $this->stylename . '/resources/main.css', 'all' );
+        $urlPackage = new UrlPackage(
+            'https://cdn.kde.org/',
+            new JsonManifestNetworkVersionStrategy('https://cdn.kde.org/aether-devel/version/manifest.json')
+        );
+
+        $out->addStyle( $urlPackage->getUrl('aether-devel/version/bootstrap.css'), 'all' );
+        $out->addStyle( $urlPackage->getUrl('aether-devel/version/aether-mediawiki.css'), 'all' );
     }
 
     /**

composer.json

+{
+    "require": {
+        "symfony/asset": "^4.3"
+    }
+}