IIRC, to set a seprate background to the toasts, you need to edit the 921 Style.
search for
code:
Element[ID=Atom(ai181)]
and add
code:
Background:rcbkd(<image id>);
ending up with
code:
Element[ID=Atom(ai181)]
{
Background:rcbkd(59002);
}
You will also need to do the same for (ai191) and (ai186)