.dropdown {
   display: none;
}
nav li:hover .dropdown {
   display: block;
}
nav { 
   background-color: aqua;
   overflow: hidden;
}
nav a { 
   float: left;
   color: black;
   text-align: center;
   padding: 14px 16px;
   text-decoration: none;
}
.dropdown a :hover{
   background-color: #ddd;
}