nav ul {
    list-style-type: none;
    padding: 0;
}

nav li {
    display: inline-block;
    position: relative;
}

nav li a {
    padding: 10px 15px;
    display: block;
    text-decoration: none;
}

nav li ul {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background-color: #fff;
    border: 1px solid #ddd;
}

nav li:hover ul {
    display: block;
}