The 404 Page Template
The 404 page template is currently a fixed part of the Help Center theme and can only be edited with custom CSS.
The 404 page template (page not found) will be shown if a link within your site refers to an article that doesn’t exist. Either the page was removed, hidden, or the user typed it incorrectly.
When users land on a 404 page, they’ll see a string of text with a link to the content source overview and a search bar, to give them some options for where to navigate next.