Fatal error: Uncaught Error: Class "Magento\Backend\Block\Widget\Tabs" not found in /var/www/magento/html/app/code/MGS/Lookbook/Block/Adminhtml/Edit/Tabs.php:11 Stack trace: #0 {main} thrown in /var/www/magento/html/app/code/MGS/Lookbook/Block/Adminhtml/Edit/Tabs.php on line 11