Dropdown Menu | WordPress Sub-Menu

/*dropdown*/
ul.sub-menu {
  position: absolute;
  width: 300px;
  background: #fff;
  list-style: none;
  margin: 0px;
  padding: 0;
  margin-top: 10px;
  opacity: 0;
  visibility: hidden;  
  transition: 0.3s;
}
ul.sub-menu li {
  border-bottom: 1px solid #ccc;
}
ul.sub-menu li a {
  display: block;
  padding: 8px 15px;
  color: #333;
}
li:hover ul.sub-menu {
  visibility: visible;
  opacity: 1;
  z-index: 99;
  margin-top: 1px;
}
ul.sub-menu li a:hover {
    color: #3452ff;
}