"How can I make a 404 page to match the rest of my site?"
If your visitors end up at a page on your site that does not exist, they will receive a standard Webs 404 page that looks like this:
Why not have a custom 404 page that matches the rest of your site?
NOTE: This only works on an account that has a custom domain name, not free sites.
Add a new blank page and simply name it "notfound."
Use the paragraph module to create a message that explains why your visitor has reached the 404 page.
Publish your page.
To make sure it works, type in a fake page address for your site into the browser. You should be re-directed to the custom 404 page.