I am seeing the same error on your mobile phone screenshot when I view your site on my MacBook Pro. The issue is coming from the fact that you have a 404 on the skin.css file i.e. it doesn’t exist.
Have you recently moved site or changed server? Is it possible for you to provide temp admin access, please? So we can take a closer look.
Also, do we have permission to disable plugins if required?
Unfortunately, I am getting an “Invalid Username” notification when attempting to log into the site. Is it possible for you to double check the username again, please?
I am at a loss as to what could have been the cause. If it happens again, can you post in this topic right away so we can look into more. I probably shouldn’t have clicked publish straight away, that way we may have been able to diagnose the issue.