Most Halloween decoration scripts assume you can edit your <body> tag. On site builders you usually can't, and a script that does document.body.classList.add(...) in the <head> throws, because the body doesn't exist yet. I ran into this while writing the install guides for halloween.js , a small library that draws spider webs in the corners of the page, blinking eyes, a flying witch, a dropping spider and a tombstone. It is MIT licensed, has no dependencies and weighs about...