Многоуровневое выпадающее меню

<div class="example">
    <ul id="nav">
        <li><a href="https://pcvector.net">Главная</a></li>
        <li><a class="fly" href="#">Статьи</a>
            <ul class="dd">
                <li><a href="https://pcvector.net">HTML / CSS</a></li>
                <li><a class="fly" href="#">JS / jQuery</a>
                    <ul>
                        <li><a href="https://pcvector.net">jQuery</a></li>
                        <li><a href="https://pcvector.net">JS</a></li>
                    </ul>
                </li>
                <li><a href="https://pcvector.net">PHP</a></li>
                <li><a href="https://pcvector.net">MySQL</a></li>
                <li><a href="https://pcvector.net">XSLT</a></li>
                <li><a href="https://pcvector.net">Ajax</a></li>
            </ul>
        </li>
        <li><a class="fly" href="#">Ресурсы</a>
            <ul class="dd">
                <li><a class="fly" href="#">Категория</a>
                    <ul>
                        <li><a href="https://pcvector.net">PHP</a></li>
                        <li><a href="https://pcvector.net">MySQL</a></li>
                        <li><a class="fly" href="#">Меню1</a>
                            <ul>
                                <li><a href="#">Меню1</a></li>
                                <li><a href="#">Меню2</a></li>
                                <li><a class="fly" href="#">Меню3</a>
                                    <ul>
                                        <li><a href="#">Меню31</a></li>
                                        <li><a href="#">Меню32</a></li>
                                        <li><a href="#">Меню33</a></li>
                                        <li><a href="#">Меню34</a></li>
                                    </ul>
                                </li>
                                <li><a href="#">Меню4</a></li>
                            </ul>
                        </li>
                        <li><a href="https://pcvector.net">Ajax</a></li>
                    </ul>
                </li>
                <li><a class="fly" href="#">Теги</a>
                    <ul>
                        <li><a href="https://pcvector.net">капча</a></li>
                        <li><a href="https://pcvector.net">галерея</a></li>
                        <li><a href="https://pcvector.net">анимация</a></li>
                    </ul>
                </li>
            </ul>
        </li>
        <li><a href="https://pcvector.net">О нас</a></li>
    </ul>
</div>

/* main menu styles */
#nav,#nav ul {
    background-image:url(../images/tr75.png);
    list-style:none;
    margin:0;
    padding:0;
}
#nav {
    height:41px;
    padding-left:5px;
    padding-top:5px;
    position:relative;
    z-index:2;
}
#nav ul {
    left:-9999px;
    position:absolute;
    top:37px;
    width:auto;
}
#nav ul ul {
    left:-9999px;
    position:absolute;
    top:0;
    width:auto;
}
#nav li {
    float:left;
    margin-right:5px;
    position:relative;
}
#nav li a {
    background:#c1c1bf;
    color:#000;
    display:block;
    float:left;
    font-size:16px;
    padding:8px 10px;
    text-decoration:none;
}
#nav > li > a {
    -moz-border-radius:6px;
    -webkit-border-radius:6px;
    -o-border-radius:6px;
    border-radius:6px;

    overflow:hidden;
}
#nav li a.fly {
    background:#c1c1bf url(../images/arrow.gif) no-repeat right center;
    padding-right:15px;
}
#nav ul li {
    margin:0;
}
#nav ul li a {
    width:120px;
}
#nav ul li a.fly {
    padding-right:10px;
}

/*hover styles*/
#nav li:hover > a {
    background-color:#858180;
    color:#fff;
}

/*focus styles*/
    #nav li a:focus {
    outline-width:0;
}

/*popups*/
#nav li a:active + ul.dd,#nav li a:focus + ul.dd,#nav li ul.dd:hover {
    left:0;
}
#nav ul.dd li a:active + ul,#nav ul.dd li a:focus + ul,#nav ul.dd li ul:hover {
    left:140px;
}