Praise be to Allah.
If attendance is optional, do not attend, so as to be free from imitation of the kaafirs in wearing this dress which is unique to them, and also to avoid the evils that are usually present in such celebrations.
The Prophet (peace and blessings of Allaah be upon him) said: “Whoever imitates a people is one of them.” Narrated by Abu Dawood, 4031, from the hadeeth of Ibn ‘Umar (may Allaah be pleased with him), and classed as saheeh by al-Albaani in Saheeh Abi Dawood.
For more information, see Question # 21643
And Allaah knows best.