Twentytwelve responsive menu toggle

I am quite new to this kind of stuff. So please bear with me.

okay. Why is that whenever I check on my website on the phone, the toggle menu’s list would go on top of the contents not like the one you would expect when you try the twenty twelve theme demo on the responsive mode. I wanted it to behave just like the demo have shown. How am I able to make it?

I’ve tried it on the desktop(responsive view), it works the way it should be but doesn’t on the actual mobile phones.