Content overlap on tablet and mobile

hi.
happy with how the desktop version of my sight looks after using the plugin, but it/i am having problems with the mobile and tablet layouts.
tablet layout is fine, but when you click the menu icon the text/links just underlay on to the site, instead of moving site down
mobile layout is weird, login / register icons get lost behind navigation bar, and same problem when you press menu icon as tablet.
am i doing something wrong or do i need some css to sort it?
any help greatly appreciated

The page I need help with: [log in to see the link]