In this case, you need to follow the previous instruction – http://prntscr.com/oquk3a
Connect to your server via FTP software, go to themes/xstore folder, there you will find 404.php file. Copy the file to themes/xstore-child folder and edit the content depends on your needs http://prntscr.com/oqul5m
Styling, can be changed using custom CSS code. Add CSS code in style.css file of the child theme. For example, http://prntscr.com/oqum70
