thrivator apologies for the late response. It seems that you have put invalid color in the appearance (something like #rgba(bla)), and Flarum accepted it without checking for errors. As a result, it broke the CSS of your website. FYI, #3936 adds a validator for this in v2.0, so I assume it is a known issue and will be fixed in a future Flarum release.
I can reproduce this easily on my forum and I get the same result. However, setting the colors back to a valid value fixed it for me - but not for your forum, for some reason. Have you maybe put a non-HEX color value anywhere else in admin?
