Overlay menu only on mobile device

I am using the responsive option of this template and the classic menu.

But I like to have the overlay menu option instead the classic, but ONLY when using a mobile / tablet device. Just like the Gavick website itself. So using desktop (standaard css file), then classic menu. When using mobile.css or small.tablet.css, then use the overlay menu.

How do I do this?

I’m afraid that modifications such as this require extensive changes to the theme’s code; I do apologize but such large changes are custom work that are beyond the scope of our technical support.