In Responsive mode, the Navigation drop down menu, (when using tab) to navigate through the menu items (not using mouse or mobile phone touch) once you tab through all the menu items and get to the last item in the nav menu, the drop down menu doesn't retreat or disappear, thereby covering the existing content on the current page. The only way to get rid of this would be to Shift tab back through and click "Skip to Content" button. For accessibility features, this should be addressed.