Fixed, the problem that you added LIVE SITE URL while installing the quickstart package. Now the site is working, however there’s a problem with your files/folder permission.

Solution: Contact your hosting provider, ask theme to chmod all files to 644 and all folders to 755

You can see a lot message related to files/folders permission on your demo site now

failed to open stream: Permission denied in

Or you can chmod files/folders by yourself using cpanel control.

Tips: https://docs.joomla.org/How_do_you_recursively_adjust_file_and_directory_permissions%3F

If you still face the issue about permission, please let me know