Набросал просто пример:
http://learn.javascript.ru/play/Loqdzb
<!DOCTYPE HTML>
<html>
<head>
<style type="text/css">
body {
background: #AAA;
}
.menu li {
cursor: pointer;
padding: 5px 15px;
}
.menu li:hover {
background: #EEE;
}
.menu ul {
background: #FFF;
box-shadow: 0 0 25px #000;
list-style: none;
margin: 20px 0 0;
opacity: 0;
padding: 0;
position: absolute;
-webkit-transition: all 0.5s;
-moz-transition: all 0.5s;
-ms-transition: all 0.5s;
-o-transition: all 0.5s;
transition: all 0.5s;
visibility: hidden;
}
.menu ul::after {
border: 14px solid transparent;
border-bottom-color: #FFF;
content: '';
left: 50%;
margin-left: -14px;
position: absolute;
top: -28px;
}
.menu.show ul {
opacity: 1;
visibility: visible;
}
</style>
</head>
<body>
<div class="menu">
Show menu
<ul>
<li>Menu 1</li>
<li>Menu 1</li>
<li>Menu 1</li>
<li>Menu 1</li>
<li>Menu 1</li>
</ul>
</div>
<script type="text/javascript">
document.querySelector('.menu').onclick = function() {
this.classList.toggle('show');
};
</script>
</body>
</html>