Single post in Important informations~

Okay, I admit it. I've tried to remember all the site rules. I've tried... and I remember there was one about site skins, and I just saw it mentioned earlier, but they didn't explain it. I've never changed my site skin, so I forgot what it was... Could someone tell me what it is? I was planning to change it soon, and I want to know the rules about it first. Thanks! Also, thanks for posting this! It's really helpful.