The words "art plain" can be interpreted in multiple ways. One possible meaning is art that is simple, unadorned or lacking detail. The antonyms for this meaning could be complex, ornate, decorative, or intricate.
Another possible meaning of "art plain" is art that is unconvincing, lacks depth, or is solely created for superficiality. The antonyms for this meaning could be convincing, persuasive, powerful, or profound.
In conclusion, the antonyms for "art plain" depend on the interpretation of the phrase. If it is understood as simple or plain art, the antonyms are complex, ornate, decorative, and intricate. If "art plain" implies a lack of depth or substance, the antonyms are convincing, persuasive, powerful, and profound.