magento-test/app/code/Magento/Ui/view/base/web/templates/block-loader.html

<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<div data-role="loader" class="loading-mask" style="position: absolute;">
    <div class="loader">
        <img src="<%= loaderImageHref %>" alt="Loading..." title="Loading..." style="position: absolute;">
    </div>
</div>