Hi, Dawn! Most of the restaurants, even the signature dining experiences, allow you to dress in pants and a nice shirt. The only exception is Victoria and Albert's, where you must dress for dinner.
We love Jiko at Animal Kingdom Lodge, and we've gone there for several of our anniversary celebrations. We also like Narcoossee's at the Grand Floridian, and you can have a nice romantic meal there.
Other restaurants you might want to consider include Artist Point at Wilderness Lodge or even Cinderella's Royal Table for a romantic dinner during the Wishes Fireworks.
One of the best and most romantic meals I've ever had was at the California Grill at the Contemporary Resort. You can't go wrong with dinner there!
Have a very happy anniversary!