Casual, so anything goes. It will be Christmas-y but edgy if you want to match that. You could wear a t-shirt and gym shorts for all we care. No judgement here.
Stereotypical Christmas! Red-white-green! But edgy! Bring your punk, emo, edgy-ness! So you can go Christmas. You can go edgy. You can go both. You can go neither. We don't care.
You are not obligated to bring a gift. Your presence is the best gift.
No.