magento-test/app/code/Magento/Backend/view/adminhtml/templates/widget/button.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
?>
<?php
/**
 * @var $block \Magento\Backend\Block\Widget\Button
 */
?>
<?= $block->getBeforeHtml() ?>
<button <?= /* @noEscape */ $block->getAttributesHtml(), $block->getUiId() ?>>
    <span><?= $block->escapeHtml($block->getLabel()) ?></span>
</button>
<?= $block->getAfterHtml() ?>