Thank you! It's working now. I modify it to below to get the right shadow and color! Many thanks!
div.header-nav-item:hover a {
text-shadow: unset !important;
}
div.header-nav-item > a:hover {
text-shadow: 3px 3px 5px #EFF193 !important;
}
.header-nav-folder-content > .header-nav-folder-item > a:hover {
text-shadow: 3px 3px 5px #EFF193 !important;
}