The fashion is actually the same every year, since Christmas Eve in France is traditionally a formal family party. Most of the time women wear a classic cocktail dress or suit. The outfit may have a touch of originality but should be kept formal, and makeup is worn a little heavier than their everyday look. Women used to go to the hair dresser, for the perfect style to look amazing during the party; but now they typically style their hair at home.
If the party is taking place at a family member’s home, most men would wear a more casual outfit than their wife. But if the family diner is at a restaurant, men would dress things up in a suit and tie, and sometimes a bow tie.