Content displaying over Navigation on mobile

Your theme is version 1.1.3 so consider updating to the latest 1.1.4

It looks like yours is a commercial theme so you should ask the vendor to resolve the issue. Their techs are best placed to tweak the stylesheet and issue a theme update. Commercial themes usually come with support included in the price.
http://codex.wordpress.org/Forum_Welcome#Commercial_Products

As a temporary fix, try this in your custom css:

/* for 800 or less */
@media only screen and (max-width:800px) {
#content {margin-top:150px}
}