So this is your current CSS:
@media (min-width: 769px) {
.main-navigation .main-nav ul li.nav-button a {
background-color: #fff;
border: 2px solid #ff4e00;
color: #ff4e00;
line-height: 40px;
}
}
Edit to this to include the hover effect and fix the height issue:
@media (min-width: 769px) {
.main-navigation .main-nav ul li.nav-button a {
background-color: #fff;
border: 2px solid #ff4e00;
color: #ff4e00;
line-height: 40px !important;
}
.main-navigation .main-nav ul li.nav-button a:hover {
background-color: #000;
border: 2px solid #ff4e00;
color: #222;
}
}