I'm running the Classifieds and Extended Events plugins with the Facebook Go theme.  I'm trying to figure out how to add icons next to the new plugin items in the menu.  I notice that for each menu item, the following css references the icon image:

.ow_main_menu .forum_forum {
background: url(images/main_forum.png)no-repeat  10pxcenter;
}
.ow_main_menu .forum_forum:hover,
.ow_main_menu .forum_forum.active {
background-image: url(images/main_forum.png)no-repeat  10pxcenter;
}
I've tried recreating this css for the classes associated with the new plugin menu items but the image is not showing up.  Currently it is inheriting a main_feault.png image which doesn't even exist.

Are there other changes I need to make to specific files?  Of note, I'm making css changes in the admin panel (not text editor to base.css); the image is definitely in the right theme image directory (in both ow_themes and ow_static); I have refreshed the browser a dozen times.

Any advice appreciated.