Extjs4 iconCls can't display in symfony

I have a project which use Extjs4 and symfony.

I put extJS source code in symonfy's web/js folder and web/css.

So i can load extjs like :

 <?php
    开发者_StackOverflow社区  use_stylesheet('ext/resources/css/ext-all.css');
 ?>

I created a formpanel and config the iconCls: 'icon-add' but it doesn't work in the page,the icon can't display.

Could you test inside firebug and try to see what ressource symfony / extJS is trying to load, you'll maybe have a network error or something like that.

How do you declare your icon-add css class?