我在管理栏菜单中添加了一个菜单，但它的样式不起作用；看起来有默认样式

 <style>

     .my_menu_item_class{
        color:red;
         background: yellow;
    }  
     </style>
 <?php   
    add_action(\'admin_bar_menu\', \'add_toolbar_items\', 100);
    function add_toolbar_items($admin_bar){
        $admin_bar->add_menu( array(
            \'id\'    => \'my-item\',
            \'title\' => \'My Item\',
            \'href\'  => \'#\',
            \'meta\'  => array(
                \'title\' => __(\'My Item\'),            
            ),
        ));
        $admin_bar->add_menu( array(
            \'id\'    => \'my-sub-item\',
            \'parent\' => \'my-item\',
            \'title\' => \'My Sub Menu Item\',
            \'href\'  => \'#\',
            \'meta\'  => array(
                \'title\' => __(\'My Sub Menu Item\'),
                \'target\' => \'_blank\',
                \'class\' => \'my_menu_item_class\'
            ),
        ));
        $admin_bar->add_menu( array(
            \'id\'    => \'my-second-sub-item\',
            \'parent\' => \'my-item\',
            \'title\' => \'My Second Sub Menu Item\',
            \'href\'  => \'#\',
            \'meta\'  => array(
                \'title\' => __(\'My Second Sub Menu Item\'),
                \'target\' => \'_blank\',
                \'class\' => \'my_menu_item_class\'
            ),
        ));
    }

?>

function load_custom_wp_admin_style($hook) {
        // Load only on ?page=mypluginname
        if($hook != \'toplevel_page_mypluginname\') {
                return;
        }
        wp_enqueue_style( \'custom_wp_admin_css\', plugins_url(\'admin-style.css\', __FILE__) );
}
add_action( \'admin_enqueue_scripts\', \'load_custom_wp_admin_style\' );