What? Then do you think all of casinos out there which providing the games from third-parties had designs from the game providers as well? I have no idea why you have such of thought but afaik the game providers only offering their games not include the design
Isn't the games designed based on the client's specification so I would say that the games that was provided have the design included. That's what my teacher said about game development, I don't know if he is right or wrong as aI haven't confirmed it.