I saw that your backed is working…
Try deactivating plugins one by one and hope you will find a solution…
Were you editing theme files or you were just updating content to the site??
Can u share the link ??
Did u added any plugin which might have cause this issue???
Can you access your site through FTP (If no, then it might be a server issue)
remove any plugin which you might have added few hours ago ??
It happened to me as well, but it was because of a plugin which i installed and suddenly my site went down…
I removed the plugin via ftp and things were back to normal!
Thanks
Keep the backup of original file before making changes, and just go for it ??
Using child theme will prevent it to get overwritten after updates. otherwise you might have to repeat the process after updation ??