@media (min-width: 768px) {
.dropdown .dropdown-menu{
    display: block; 
  opacity:0;
-webkit-transition: all 200ms ease-in;
-moz-transition: all 200ms ease-in;
-ms-transition: all 200ms ease-in;
-o-transition: all 200ms ease-in;
transition: all 200ms ease-in;
}
.dropdown:hover .dropdown-menu {
    display: block;
    opacity: 1;
}
}

Why media queries? Because you don’t want display:block on hover on the mobile menu (as the hover used for this would double the submenu). As for CSS transitions, you can generate them using any of the online generators, such as this one.

Post Adding CSS transition on Bootstrap drop-down menu je prvi puta viđen na bbird.me.