When you run the W3C Markup Validation Service on a page with a custom contact form, you get an error:
Line 218, Column 23: document type does not allow element "style" here
The element named above was found in a context where it is not allowed. This could mean that you have incorrectly nested elements -- such as a "style" element in the "body" section instead of inside "head" -- or two elements that overlap (which is not allowed).
There is also an error about a
<form> being inside an inline element.