The only real "code" is no bathing suits, or tank tops on men. I suppose you'd also need shoes. Absent that, the only code is one that you'd impose on yourself.
When you make PS, they may tell you "business casual" or "smart casual", but that's merely a "suggestion", not any sort of requirement.
Many people do dress up a bit at CG and many suggest they feel out of place otherwise. But we always go "Theme park casual" and it's simply never been a problem. Dined there that way about 7 times now, and never ever felt out of place.