Hello, @Alessandro,
Simply go to the Dashboard >> XStore >> Theme Options >> Theme Custom CSS and then paste the below code at the bottom of the CSS box.
.nav-sublist-dropdown .container{height: 100% !important; overflow-y:scroll !important;} #header-vertical .et_b_header-menu li>.nav-sublist-dropdown:not(.nav-sublist){top:10% !important;}
Then save settings and check back to your site after clearing the browser cache.
Regards 8Themes Team.
