سلام عليكم
I want to tell up small of what i know about the relationship between islam and crismas.
Allah said in the holy book: the food of the people of the book is lowful unto you and your food is lawful unto them...
From this injunction Allah did not prohibit muslims from eating the food of the jews and the cristians (you can eat the crismas food given to you)
But you are not adverce to say happy crismas or celebrat crismas as a muslim because these people are either celebrating the Allah (God) was born (given birth to) or when Allah (God) son was born (given birth to) subhanallah. He you gifted a crismap gift or food collect it but don't wish,celebrat or appretiate them for what they are doing. Pls if made any mistake correct me.
سبحانك لله و بحمدك أشهد أن لاإلاهال أنت أستخفرك و أتوبإلىه