public function getRequiredCSSFiles()
    {
        $files = [];
        
        foreach (ClassInfo::subclassesFor(ContentController::class) as $controller) {
            
            if ($required_css = Injector::inst()->get($controller)->getRequiredCSS()) {
                
                foreach ($required_css as $file) {
                    
                    $file = ModuleResourceLoader::singleton()->resolvePath($file);
                    
                    if (!isset($files[$file])) {
                        $files[$file] = file_get_contents(Director::getAbsFile($file));
                    }
                    
                }
                
            }
            
        }
        
        return $files;
    }