The actual answer, according to Carnival's website:
The steakhouse has an intimate but fun atmosphere, so it can be as romantic for couples as it can be comfortable for family dinners. For all the elegance Steakhouse offers, why not dress the part? The dress code for Steakhouse is the same as the evening’s onboard dress code: either cruise casual or cruise elegant. Here are the quick differences — and remember, no shorts allowed in Steakhouse:
Cruise casual for women: casual and summer dresses, skirts, pants, Capri pants and nice jeans
Cruise casual for men: sports slacks, khakis, nice jeans, collared sport shirts
Cruise elegant for women: cocktail dresses, pantsuits, elegant skirts and dresses or an evening gown if you wish
Cruise elegant for men: dressy slacks and shirts, and a sports coat is suggested; suits and ties or tuxedos also welcome