better_page_not_found

This module automatically improves the layout of 404 (page not found)
and 401 and 402 (not authorized) pages. If the current page is an 404
(or 401 or 402) page then it replaces the page content with a themed
message.
It does not replace other page items, so the error page will
still show your header and footer, and thus have your site styling intact.

The 404 (page not found) page will show following message:
'The requested page could not be found.' (this is translatable)

The 401 and 402 (not authorized) pages will show following message:
'Sorry, you are not authorized to access this page.' (this is translatable)

Under each message, a button 'Go to homepage' is added automatically.

If you want you can further style these messages by targeting following
classes in your css:
- .c-system-message (wrapper around the message)
- .c-system-message__text (text itself)
- .c-system-message__button (the button to the homepage)