This 404 error page project is an exercise in creativity, design, and fun use of CSS & HTML to create interesting, tolerable 404 pages, rather than the standard run of boring 404 error pages which do nothing for the user.
A good 404 page is visually interesting, fits with the rest of the site, and provides relevant information beyond the message "404 error" which is often meaningless to less experienced users. Poor 404 pages can turn users off from a site.
Of course, how and how often a user reaches a 404 page is another matter entirely, and no creative design of a 404 error page can help solve those fundamental issues, but at least we can have some fun getting the 404 error side of things cleaned up.