Simply change body height < 300px (height of mobile viewport on landspace is around 300px to 500px)
JS
$( '.offcanvas-toggle' ).on( 'click', function() {
$( 'body' ).toggleClass( 'offcanvas-expanded' );
});
CSS
.offcanvas-expended { /* this is class added to body on click */
height: 200px;
}
.offcanvas {
height: 100%;
}