Looks like you 'fixed' your doctype -it's now complete, but you picked the wrong one. You're not using frames (which is a good thing - NEVER use frames) so don't use the frames doctype - go with HTML 4.01 strict.
Your meta tags aren't closed, there's a div tag between the and the tag, and that's just the beginning of the errors you should clean up.
Using
is also not the best way to go- for one, is already bolded, but if you want to style if further, use the external CSS.
In you CSS, it's not necessary to set your background color for every element - just pick the main one (in your case: centerdoc, change, and navigation), everything else will be just that - so you only have to mention it again, if you want something in a DIFFERENT color.