Mrs, on the Enchantment, there's not much difference between "smart casual" and "casual." Dinner dress is basically "formal" and "not formal."
The "official" rule for the dining room at dinner is no jeans (although some still wear jeans) and no shorts. I usually think of it as the type of clothing one would wear out to a restaurant, and I can't go wrong that way. Jackets are not needed on the non-formal nights.