What does this mean?
Doctype is the first element in the source code of a web page and should be part of every HTML document. Without one your browser enters a rather strange mode.
It looks like you don’t have a Doctype, and while you can fix this yourself, it’s a little tricky unless you know how to code.
We suggest sending this issue to your developer to resolve.
To learn more visit: https://alistapart.com/article/doctype/