With the system page 404 - Page not found you can adapt this error message page to the style of your own website.
A 404 - Page not found message is generated when a visitor visits a page that no longer exists. The 404 - Page not found error message is a server notification and is given by a web server when the requested file (page) does not exist.
The systempage 404 - Page not found has a normal text widget where you can adjust text if you'ld like.
icon in the right upper corner of the text widget to adjust the content. 