If you’re wanting to push your custom sub-menu link to the top of the list within a WordPress menu, you can use this code to ensure that you’re always the alpha sub-menu item.

function custom_menu_order(){
    global $submenu;
	  
    $find_page = 'themes.php';
    $find_sub = 'Widgets';
    
    foreach($submenu as $page => $items):
        if($page == $find_page):
            foreach($items as $id => $meta):
                if($meta[0] == $find_sub):
                    $submenu[$find_page][0] = $meta;
                    unset ($submenu[$find_page][$id]);
                    ksort($submenu[$find_page]);
                endif;
            endforeach;
        endif;
    endforeach;
}
add_action('_admin_menu', 'custom_menu_order');

View the SE thread where I originally posted this.