Hi,
I could not access your website backend with the provided account. So please add the below CSS rules to the custom.css file to solve the background issue.
@media (max-width: 991.98px) {
.nav-breakpoint-lg .t4-megamenu {
background: #0C720D;
border: 0;
border-top: 1px solid rgba(0,0,0,0.1);
}
}
Save and reload your website to view the update.
If you have any questions, please let us know.
Regards.