If a page on your site doesn't load, an error message shall be displayed to the site visitor. As there are different errors, there are different pages which will display, but what's standard for all of them is that they're generic and most likely shall have absolutely nothing that is similar to the layout of your site, which may be annoying for any site visitor. This is the reason why website hosting service providers have introduced a function called Custom Error Pages. For a number of different errors, site visitors shall see your custom made content, which could be informative or witty, based on your choice, and which shall match the design of your website, so the pages will not look like they aren't part of your site at all. You can use this option for many errors - 400 (Bad request), 401 (Unauthorized), 403 (Forbidden) and 404 (File not Found).
