To create dropdown menu hover effect, you can use this code to Custom CSS box
div.header-nav-folder-content {
padding: 0px !important;
}
div.header-nav-folder-item {
padding-right: 1em !important;
padding-left: 1em !important;
}
div.header-nav-folder-item:hover {
background-color: #fff;
}
div.header-nav-folder-item:hover a {
color: #000 !important;
}
Result
