.open > .dropdown-menu {
opacity:1; visibility:visible; 
}
.dropdown:hover .dropdown-menu, .btn-group:hover .dropdown-menu { opacity:1; visibility:visible; }
.dropdown-menu {
opacity:0;
display:block;
visibility:hidden;
transition: all 0.2s ease-out 0.5s;
-webkit-transition: all 0.2s ease-out 0.5s;
}
.navbar-default .navbar-nav > li.dropdown:after{
opacity:0;
visibility:hidden;
display:block;
transition: all 0.2s ease-out 0.5s;
-webkit-transition: all 0.2s ease-out 0.5s;
}
.dropup .dropdown-menu {
-webkit-transform-origin: bottom;
transform-origin: bottom;  
}
.navbar .nav > li > .dropdown-menu:after {
}