css制作简易导航栏，但是不知道为什么不成功
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>导航栏</title>
<style>
.nav{
background-color: #00aba9;width: 100px;height: 40px;text-align: center;line-height: 40px;
}
.main{
width: 100px; height: 100px; background-color: pink;text-align: center;line-height: 100px;display: none;
}
.nav:hover .main{display: block;}
</style>
</head>
<body>
<div class="nav">导航</div>
<div class="main">小菜单</div>
</body>
</html>