What do I wear to a Chabad Seder?

I’m a secular Jew and I’ve actually never attended a Seder before. I’m a female. What should I wear? I know I need to cover my knees, collarbone, and elbows. But, what about fabrics/materials, colors, and level of formal dress? Also, what should I put my non-Jewish husband in, other than a kippa? And, because I am married, should I wear a headscarf?

Thank you in advance! I’m stressing out!