This may sound like a silly question, but I'm having a bit of confusion. 

I'm not sure what to say. I work remotely and I am a member of a team on the opposite side of the earth. On the chat, when they say “good morning” or “good night”, I get confused about what I should reply because when they are enjoying morning it is night for me.

Should I say “good morning” when they say “good morning”? Can I say “good morning” to them when it's morning for me? Thanks!!