Too many HTML errors that even the validator suppressed all past Line 664, Column 187.
Although there were 275 CSS errors reported, ignore any of the CORRECT CSS 3 rules that are flagged.
Not sure the scroll:navigation is a big problem as most people will select a page from the nav menu first without scrolling. Setting the nav menu so it isn't fix is one solution you may not like. Possibly clean up errors so all browsers are as close as can be "on the same page". Then a solution might be found.