Instead of standard messages, a user may see a well-designed page with customized navigation elements.
No matter how hard you try fixing all the errors, users will occasionally bump into your 404 page for one reason or another. That’s why your main goal is to provide a user with a rather pleasant experience.
First, let’s take a look at Google’s recommendations to create the right 404 pages:
Notify users in a polite form that the requested page is not available.
Design a 404 page in the same way as other pages of the website. Navigation elements should look the same too.
Link your 404 page to the most popular articles or comment sections, as well as to the main page.
Provide users with an opportunity to report broken links.
Even if your 404 page is useful and looks great, you don’t want it to appear in Google search results. Make sure that the webserver returns an actual 404 HTTP status code when a missing page is requested. It is necessary to prevent such pages to be indexed by search engines.