Hi!
Try adding this custom css:
@media only screen and (max-width: 719px) {
#nav-header.nav-container { border-top: 1px solid #eee; border-bottom: 1px solid #eee; }
#nav-header .nav-toggle { border-left: 1px solid #eee; color: #444; -webkit-box-shadow: none; box-shadow: none; }
}The reason you have trouble there is because the menu wasn't really designed to work with white as color.