magento-test/app/code/Magento/MediaGalleryUi/view/adminhtml/web/template/image-uploader.html

<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<div class="media-gallery-image-uploader-container">
    <form id="image-uploader-form" class="no-display" method="POST" enctype="multipart/form-data">
        <input afterRender="initializeFileUpload" id="image-uploader-input" type="file" name="image"
               multiple="multiple"/>
    </form>
    <div data-role="spinner" class="admin__data-grid-loading-mask" visible="loader">
        <div class="spinner">
            <span repeat="8"></span>
        </div>
    </div>
</div>