do not expose a new UI and check on library id

core/lib/Drupal/Core/Asset/AssetResolver.php

@@ -222,7 +222,6 @@ public function getCssAssets(AttachedAssetsInterface $assets, $optimize, ?Langua
       $definition = $this->libraryDiscovery->getLibraryByName($extension, $name);
       foreach ($definition['css'] as $options) {
         $options += $default_options;
-
         // Copy the asset library license information to each file.
         $options['license'] = $definition['license'];
 

core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php

@@ -227,7 +227,9 @@ public function buildByExtension($extension) {
             $options['group'] = JS_LIBRARY;
           }
           elseif ($type == 'css') {
-            $options['group'] ??= $extension_type == 'theme' ? CSS_AGGREGATE_THEME : CSS_AGGREGATE_DEFAULT;
+            // Component stylesheets should be added in the "theme" aggregate
+            // group to load them alongside the theme.
+            $options['group'] = ($extension_type == 'theme' || str_starts_with($id, 'components.')) ? CSS_AGGREGATE_THEME : CSS_AGGREGATE_DEFAULT;
           }
           // By default, all library assets are files.
           if (!isset($options['type'])) {

core/lib/Drupal/Core/Theme/ComponentPluginManager.php

@@ -187,10 +187,7 @@ protected function libraryFromDefinition(array $definition): array {
       TRUE
     );
     if ($css_file) {
-      $library['css']['component'][$css_file] = [
-        // Without casting to a string, Twig rendering breaks due to integer.
-        'group' => (string) CSS_AGGREGATE_THEME,
-      ];
+      $library['css']['component'][$css_file] = [];
     }
     $js_file = $this->findAsset(
       $component_directory,