Move your mouse around the image on Github’s 404 page to see the parallax effect. This is not the web page you are looking for.
Github gives their best practices for error pages and a list of all their error pages, like:
500: An exception occurred and we couldn’t recover. (Oops! Octocat is falling off a cliff.)
503: Unicorn! We are having a bad problem and the app server will not talk to us.