how to keep the container fixed?

[dcalixto]

I would like to know how to keep the container fixed below the menu when hover like:

www.iherb.com

How how to keep the menu below fixed?

I've tried this

$(document).ready(function() {
    $("#main-nav").menuAim({
        rowSelector: "li.parentnav",
        submenuDirection: "below",

        tolerance: 0,
        exitMenu: function(){return true;},
        activate: function(a){
            $(a).children('.subnav').show();
        },
        deactivate: function(a){
            $(a).children('.subnav').hide();
        }
    });
});