I agree with the other posters. Celebrity is no jeans in the dining room. If you had said you were on Carnival I would have said it was fine. Carnival doesn't prohibit jeans in the dining room. However, you are on Celebrity they clearly prohibit jeans in the dining room. I would not risk being turned away.
I disagree a little with Norm. A cocktail dress is not
required on informal nights on Celebrity this line is not quite that formal. In fact that gets a bit confusing for Celebrity on the difference bewteen Causal and informal nights for women. Because nice slacks are allowed on both nights. I just paired it with nicer blouses on informal nights. I did a 12 day with Celebrity to Alaska. I hope that helps.