Dressing up for Celebrity Vigin cruiser

[namklov]

I am taking a cruise on Summit on 3/22. I have been on about 10 cruises, but never on Celebrity. I really like Norwegian's less formal approach to meals and dressing, so I am not to sure what to expect from this cruise. I have read that people have been turned away from dining rooms because their attire was not appropriate for formal and semi formal nights. I don't plan on showing up in capris or short skirts, but do I have to wear a dress on these nights. I plan on black pants and dressier tops. IS that OK? Is there really that much of adifference between what is worn on formal nights and what is worn on semi formal nights? Please help, I am running out of time and the group I am traveling with is in a panic!!!!!