Changing broadcaster group="sidebar"

[matinte]

Hi!
I have an overlay where my app is declared as a sidebar but I would
like to change it's appearance so it would look like the zotero
plugin, for example. This is my code now:
<broadcasterset id="mainBroadcasterSet">
<broadcaster id="app_id"
label="app_name"
type="checkbox"
group="sidebar"
sidebarurl="chrome://app/content/app.xul"
siderbarTitle="title_app"
oncommand="toggleSidebar('app_id');"/>
</broadcasterset>

Does anybody knows another value for group so I can change the
"sidebar" appearance? Is there another way to change it?

Thanks in advance :D