Fatal error: Uncaught Error: Interface "Magento\Framework\Event\ObserverInterface" not found in /var/www/magento/html/app/code/BBNT/Base/Observer/SiteCss.php:22 Stack trace: #0 {main} thrown in /var/www/magento/html/app/code/BBNT/Base/Observer/SiteCss.php on line 22