making GWT's toolbarbutton icon appear

[bryan lim]

hi all,

i was told that i can post gwt related questions here and it seems that my posts on the same question( for the past few times) have been taken away. if this is not the right forum, can someone please tell me where should i ask the gwt-question then?
i am posting here as i can't get an answer in gwt forum.

anyway,

i have this toolbarbutton and its method setIconCls();

    ToolbarButton button_daily_View = new ToolbarButton("Daily View");
      button_daily_View.setIconCls("database-add-icon");

at the css, i have this:

.database-add-icon{
        background-image:url(images/database_add.png);

} 

but the icon don't appear. I am not sure what went wrong. maybe it's not the gwt fault but i cannot pin-point where is the error? can someone advise me ? I attached a picture ( circled the point where icon supposed to be) THANKS alot!!