Dropdown not working

Dropdown doesnt seem to be working as it drags down the other part of the <ul>

HTML

<body>
   <div class="nav">
       <ul>
           <li>
               <a href="#">PAGE</a>
               <ul>
                   <li><a href="#">DROPDOWN</a></li>
                   <li><a href="#">DROPDOWN</a></li>
               </ul>
           </li>
           <li><a href="#">PAGE</a></li>
           <li><a href="#">PAGE</a></li>
           <li><a href="#">PAGE</a></li>
       </ul>
   </div>
</body>

CSS

* {
    padding: 0;
    margin: 0;
    border: 0;
}

html, body {
    height: 100%;
    width: 100%;
    font-family: 'Open Sans', sans-serif;
}

h1 {
    font-weight: 100;
}

.nav {
    width: 100%;
    height: 10%;
    background-color: #333;
    text-align: center;
    position: fixed;
    z-index: 150;
}

.nav ul {
    height: 100%;
    width: 100%;
}

.nav > ul > li {
    display: inline-block;
    list-style: none;
    margin: 0 20px 0 20px;
}

.nav > ul > li:first-child > a:after {
    width: 6px;
    height: 6px;
    border-bottom: 1px solid white;
    border-right: 1px solid white;
    position: absolute;
    margin-top: calc(5vh - 5px);
    margin-left: 8px;
    content: "";
    transform: rotate(45deg);
}

.nav > ul > li > ul {
    display: none;
}

.nav > ul > li > ul > li {
    list-style: none;
    background-color: #333;
    padding: 0 15px 0 15px;
}

.nav li:hover > ul {
    display: block;
}

.nav ul a {
    color: #A3ABA3;
    text-decoration: none;
    line-height: 10vh;
}

.nav a:hover {
    color: #FFF;
}

@media only screen and (max-device-width: 480px){
    
}