WordPress Files Corrupted

Currently re-doing a site for a client. Built the whole site on my Mac using MAMP and just uploaded it to a separate part of their website to do some testing and tweaking before we replace the existing site. It was working fine but I went on yesterday and the whole site looked a little weird on my phone. I then logged into the Admin section and it looks the same, so I am guessing that some WordPress files got deleted or something. It’s strange because I didn’t change anything and I am the only person with access to the files. Any suggestions on what to try? Thanks!

Site link: old.coresusquehanna.org