An unexpected error occurred while i was using the Theme Editor. I added display: none;" under page meta, as well as breadcrumbs. Now I cannot get into the webpage at all. I cannot login either.

This is the error:
File /home2/liveunit/public_html/Main/themes/slate/default.php not found. All themes need default.php and view.php files in them. Consult concrete5 documentation on how to create these files.

Here is the page:
http://173.254.67.225/Main/

I need help getting the page back up. This is for non-profit. My colleagues and I have put hard work into this page and it would be a shame to start from scratch.