Does anyone know where the content lives for the PageNotFound page?
I see in the "ErrorLayout" there is a
class="error-content" section. I would like to edit the content for this section.
Assuming a publishing site.
In the Pages library of the rootsite there is a page called "PageNotFoundError.aspx". Just like a regular page. Edit this page to change the content of the PageNotFound page.
Even more simpler: Trigger a PageNotFound error and hit "Edit Page" in the SiteActions menu.