newsupernova/vendor/magento/module-tax/view/adminhtml/templates/toolbar/class/add.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
?>
<div data-mage-init='{"floatingHeader": {}}' class="page-actions">
    <button type="button" onclick="window.location.href='<?= /* @escapeNotVerified */ $createUrl ?>'">
        <?= /* @escapeNotVerified */ __('Add New Class') ?>
    </button>
</div>