newsupernova/vendor/magento/module-theme/view/adminhtml/page_layout/admin-empty.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<layout xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_layout.xsd">
    <container name="root">
        <container name="page.formkey" as="page.formkey"/>
        <container name="content" as="content"/>
        <container name="js" as="js" label="JavaScript"/>
    </container>
</layout>