Thank you for your reply.
What I mean is: the 404 page has nothing from the theme. I want the 404 page (404.php) to be like the site with the header and footer so visitors who land on a 404 don’t get completely lost – have the feel that they are still on the same site and have a chance to go back somewhere else through the menu.
I managed to add the header and footer but I totally not sure of the code so I don’t want to see a disaster down the road because I screwed up something.
Frankly, just saying, that would be nice to have an editable 404 page that my clients could edit in the editor, like any other page, with the same theme all around the “page not found’ text. May be you could put that in the Theme suggestion box?
THANK YOU 🙂