can i get your site link and the problem you find in the mobile version? . I think there is z index problem, go to additional CSS > copy-paste below CSS

let me know it works or not: if it does not work please mail us at amplethemes@gmail.com . we will help you

//css code

.main-menu.clearfix {
background: #000;
z-index: 99999999;
}
div#primary {
z-index: 99999;
}