Adding Back End Assets

In some cases you might want to adjust the default back end stylesheets or add additional stylesheets or JavaScript for your back end modules. As outlined in the asset management framework article, you can inject additional assets for the back end via the following global arrays:

Array Description
$GLOBALS['TL_CSS'] Additional stylesheets for the <head>.
$GLOBALS['TL_JAVASCRIPT'] Additional JavaScript files for the <head>.
$GLOBALS['TL_MOOTOOLS'] Additional HTML code at the end of the <body>.

Adding additional entries to these arrays can be done in many ways. This guide will outline two general use cases, in order to give an idea what is possible.

Starting with version 4.11 global assets can now be added via the config/config.yaml: Additional back end settings

Adding Assets Globally

If you need assets globally in the back end, e.g. when customizing the back end theme, then one way to ensure that your assets are inserted on every back end page is to use a Symfony kernel event and then check for the Contao back end scope there. The following example implements an event subscriber for this purpose using the kernel.request event in order to add a Font-Awesome kit to the back end.

// src/EventSubscriber/KernelRequestSubscriber.php
namespace App\EventSubscriber;

use Contao\CoreBundle\Routing\ScopeMatcher;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;

class KernelRequestSubscriber implements EventSubscriberInterface
    protected $scopeMatcher;

    public function __construct(ScopeMatcher $scopeMatcher)
        $this->scopeMatcher = $scopeMatcher;

    public static function getSubscribedEvents()
        return [KernelEvents::REQUEST => 'onKernelRequest'];

    public function onKernelRequest(RequestEvent $e): void
        $request = $e->getRequest();

        if ($this->scopeMatcher->isBackendRequest($request)) {
            $GLOBALS['TL_JAVASCRIPT'][] = '';

Adding Assets for a DCA

In other cases it might be sufficient to add additional assets only for a specific DataContainer view, e.g. when you created a custom content element and want to style its appearance in the back end. In that case you can also use the onload DCA callback for the specific DCA.

// src/EventListener/DataContainer/ContentOnLoadCallbackListener.php
namespace App\EventListener\DataContainer;

use Contao\CoreBundle\DependencyInjection\Attribute\AsCallback;

#[AsCallback(target: 'config.onload', table: 'tl_content')]
class ContentOnLoadCallbackListener
    public function __invoke(): void
        $GLOBALS['TL_CSS'][] = 'files/path/to/my.css';