The easiest way of conceptualizing the base and superstructure is to just say base = economics and superstructure = politics. Avoid the temptation of trying to conceptualize the superstructure as some nebulous notion of culture, arts, or ideology. Jumping immediately to Gramsci is a mistake. They compose part of the superstructure, but the superstructure isn't only that. The superstructure is also political parties, the government, the media, the military, and law enforcement. Religion is part of the superstructure, but it's not just religious text or dogma, but the actual material religious institution and organizations as well.

People internalizing capitalist realism is the capitalist superstructure maintaining the capitalist base, but pinkertons beating the shit out of striking workers so scabs can cross the picket line or pigs destroying homeless encampments and forcing them on a death march is also the the capitalist superstructure maintaining the capitalist base. The superstructure is as material as the base and the way in which the superstructure maintains the base is material as well. Reagan firing striking air traffic controllers and getting the national guard to fill in as scabs is a good example of the superstructure (national guard) maintaining (filling in as scabs) the base (air traffic controllers as a form of wage labor).

It also means socialist art is insufficient towards countering the capitalist superstructure because the capitalist superstructure is not just capitalist art. Producing good socialist art with a principled anti-capitalist or anti-imperialist message isn't stopping the pigs from blinding people with "less than lethal" rubber bullets. For that, you would need to build a counter-superstructure that's more substantial than art.