/* Hide Dropdowns by Default
 * and giving it a position of absolute */
nav ul ul {
    display: none;
    position: absolute;
    top: 100%;
}

/* Display Dropdowns on Hover */
nav ul li:hover > ul {
    display:inherit;
}

/* Fisrt Tier Dropdown */
nav ul ul li {
    min-width:170px;
    display:list-item;
    position: relative;
}