To change default error pages, simply create your own html files — upload them to your server, and add the following to your .htaccess file: (source)
ErrorDocument 400 /errors/badrequest.html ErrorDocument 401 /errors/authreqd.html ErrorDocument 403 /errors/forbid.html ErrorDocument 404 /errors/notfound.html ErrorDocument 500 /errors/serverr.html
You are welcome to use the ones I’ve created (links & image previews below). I’ve used SVG as background images as I wanted them to be scalable — you can replace with any image type you want. Note: that SVG is only supported by recent browsers.
Download zip — contains 5 html files and 5 svg files (all the code is simple and validates)
Check out the example page links: (re-size browser to see how sharp the svg re-sizes)
If using SVG (as in my example) you will need to make sure the remote server sends the appropriate MIME type so these lines may need to be added to .htaccess file: (source)
AddType image/svg+xml svg AddType image/svg+xml svgz