404 Page Styling and/or Changes
For the 404 page you have a few options:
- If you just duplicate the index.php file in the root directory of the theme and rename it to 404.php then it will become your 404 page template that you can directly edit as you see fit.
- If you want to use the theme's meta box page builder to design a 404 page that way, then you'd want to create a page and setup all 404s to redirect to that page. This plugin can assist with that: https://wordpress.org/plugins/404-to-301/
- Or there's also this plugin that can be used to create a custom 404 page, which would be simpler with fewer features than the above option: https://wordpress.org/plugins/404-page/