Header menu and styling has disappeared

I was just contacted by a client who has not been on their site in weeks. Their main menu has completely disappeared and all the styling for their header is gone. I have already gone through and turned on/off all the plugins and cannot find anything causing a conflict. Has anyone seen this happen before? This is very strange and currently I cannot find anything that has changed on the site. I will post the website below in the private content and if you want credentials let me know. I just wanted to see if this was some bug or something first.