magento-test/app/code/Magento/Backend/view/adminhtml/templates/page/notices.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
?>
<?php
/**
 * @see \Magento\Backend\Block\Page\Notices
 */
?>
<?php if ($block->displayNoscriptNotice()) : ?>
    <noscript>
        <div class="messages">
            <div class="message message-warning message-noscript">
                <strong><?= $block->escapeHtml(__('JavaScript may be disabled in your browser.')) ?></strong>
                <?= $block->escapeHtml(__('To use this website you must first enable JavaScript in your browser.')) ?>
            </div>
        </div>
    </noscript>
<?php endif; ?>
<?php if ($block->displayDemoNotice()) : ?>
    <div class="messages">
        <div class="message message-warning message-demo-mode">
            <?= $block->escapeHtml(__('This is only a demo store. You can browse and place orders, but nothing will be processed.')) ?>
        </div>
    </div>
<?php endif; ?>