Arc-hive-omeka-theme/view/common/cross-site-search/fulltext-form.phtml

<?php
$action = $action ?? $this->url(null, [], true);
$fulltextSearch = $fulltextSearch ?? $this->params()->fromQuery('fulltext_search');
?>

<form action="<?php echo $this->escapeHtml($action); ?>" class="sitewide-search-form">
    <input type="text" name="fulltext_search" value="<?php echo $this->escapeHtml($fulltextSearch); ?>">
    <input type="submit" value="<?php echo $this->escapeHtml($this->translate('Search')); ?>">
</form>