My 18 year old son is having a bunch of friends over in his bedroom... His taste in music... Classical! I just heard them all singing to

Classical though? It's not Classical in the strict sense, nor "classical" generically.

It might be a "classic" of its time, at least in sales, the Big Band and crooning era of American, light "popular" music. I do have misgivings about that third adjective as it implies - wrongly - that any other style is not popular..