Fix navigation stacking on docs pages

- Add z-index: 1000 to the sticky nav container so it renders above other positioned elements

Author: ndoschek

src/components/Nav.js

@@ -28,6 +28,7 @@ const StyledNav = styled.div`
         top: 0;
         left: 0;
         right: 0;
+        z-index: 1000;
     }
 
     .nav {