Add new icon to jQuery Easy UI

I want to add new icons to my jquery easy UI, but I create a new class in the ribbon-icon.css and put the class on the data options and doesn't work. Whats wrong in my code? Code in the html:

 <a href="#" class="easyui-linkbutton" data-options="name:'concurso', iconCls:'icon-concurso-large', iconAlign:'top',size:'large', plain:'true'">Concurso</a>

Code in the css:

.icon-concurso-large{
background:url('images/32/concurso.png') no-repeat center center;
}

I know that it's old question, but as mentioned - "for future Googlers":

1. Put a new class in your CSS, for example:

   .icon-warning {
        background: transparent url("../img/warning.png") no-repeat scroll center center;
    }
   

2. Set iconCls to your class ("icon-warning" from above example)

3. Make sure that your CSS is loaded AFTER jquery-easy-ui's CSS (otherwise your class will by overwritten)