修改/includes/templates/marcus/common/tpl_drop_menu_mobile.php
把第二个<li>的内容也就是

<span class="name">
<a href="#"><span class="act-underline"><?php echo HEADER_TITLE_CATEGORIES; ?></span></a>

<?php
    //Display Categories
    echo $pzen_menu['simple'];
?>

改成

<?php
// 顶级分类直接作为一级菜单项输出
$cats = $db->Execute("
  SELECT c.categories_id, cd.categories_name
  FROM " . TABLE_CATEGORIES . " c
  JOIN " . TABLE_CATEGORIES_DESCRIPTION . " cd
       ON cd.categories_id = c.categories_id
      AND cd.language_id = " . (int)$_SESSION['languages_id'] . "
  WHERE c.parent_id = 0
    AND c.categories_status = 1
  ORDER BY c.sort_order, cd.categories_name
");

while (!$cats->EOF) {
  $cid  = (int)$cats->fields['categories_id'];
  $name = htmlspecialchars($cats->fields['categories_name'], ENT_QUOTES, CHARSET);

  echo '<li><a href="' . zen_href_link(FILENAME_DEFAULT, 'cPath=' . $cid) . '">' . $name . '</a></li>';

  $cats->MoveNext();
}
?>