Too much work for Cspace to change the site's layout just for holidays.

For regular holidays, there's always a thread made about it on the forums of course. As for original holidays, I dunno, I vaguely remember Cspace making something about SeeD's Anniversary one time, so that's basically a unique one here.
Someone creative enough could make something cool-lookin' (image/screenshot) for holidays, like an image in Photoshop, or something in a game (still being done in-game I believe). I remember I used to make symbols for holidays out of fires in RuneScape, and I made some weird pink swirl thing for Valentine's once. Just some examples, those things are always available to do. Going farther than that isn't really necessary since it's just one day. If you had a specific idea on how to go further feasably, then things could possibly work out.