stack overflow drop down

HTML

<nav>
    <ul class="menu">
        <li><a href="#">link</a></li>
        <li><a href="#">link</a></li>
        <li><a href="#">link</a>
            <ul>
                <li><a href="#">link</a></li>
                <li><a href="#">link</a></li>
            </ul>
        </li>
        <li><a href="#">link</a></li>
    </ul>
</nav>

CSS

body {
    background: mediumSeaGreen;
}

nav {
    background: -webkit-gradient(linear, center top, center bottom, from(#fff), to(#ccc));
    background-image: linear-gradient(#fff, #ccc);
    border-radius: 6px;
    box-shadow: 0px 0px 4px 2px rgba(0,0,0,0.4);
    padding: 0 10px;
    position: relative;
}

.menu {
    height: 40px;
    width: 100%;
    
}

.menu li {
    float: left;
    position: relative;
    list-style-type: none;
     /*background: url('img/denim.png');
    font-family: 'Droid Sans', sans-serif;*/
}

.menu li a {
    color: #444;
    display: block;
    font-size: 14px;
    line-height: 20px;
    padding: 6px 12px;
    margin: 8px 8px;
    vertical-align: middle;
    text-decoration: none;
}

.menu li a:hover {
    background: -webkit-gradient(linear, center top, center bottom, from(#ededed), to(#fff));
    background-image: linear-gradient(#ededed, #fff);
    border-radius: 12px;
    box-shadow: inset 0px 0px 1px 1px rgba(0,0,0,0.1);
    color: #222;
}

/* Dropdown styles */

.menu ul {
    position: absolute;
    left: -9999px;
    list-style: none;
    opacity: 1;
    transition: opacity 1s ease;
}



/* Displays the dropdown on hover and moves back into position */
.menu li:hover ul {
    background: rgba(255,255,255,0.6);


    left: 5px;

}