Выпадающее меню

<div class="example">
    <ul id="nav">
        <li class="current"><a href="https://pcvector.net">Главная</a></li>
        <li><a href="https://pcvector.net">Статьи</a>
            <ul>
                <li><a href="https://pcvector.net">HTML / CSS</a></li>
                <li><a href="https://pcvector.net">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 href="https://pcvector.net">Ресурсы</a>
            <ul>
                <li><a href="https://pcvector.net">Категория</a>
                    <ul>
                        <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 href="https://pcvector.net">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 {
    display:inline-block;
    width:100%;
    margin:0px auto;
    padding:0;
    background:#335599 url(../images/bg.png) repeat-x 0 -110px;

    border-radius:10px; /*some css3*/
    -moz-border-radius:10px;
    -webkit-border-radius:10px;
    box-shadow:0 2px 2px rgba(0,0,0, .5);
    -moz-box-shadow:0 2px 2px rgba(0,0,0, .5);
    -webkit-box-shadow:0 2px 2px rgba(0,0,0, .5);
}
#nav li {
    margin:10px;
    float:left;
    position:relative;
    list-style:none;
}
#nav a {
    font-weight:bold;
    color:#e7e5e5;
    text-decoration:none;
    display:block;
    padding:8px 20px;

    border-radius:10px; /*some css3*/
    -moz-border-radius:10px;
    -webkit-border-radius:10px;
    text-shadow:0 2px 2px rgba(0,0,0, .7);
}

/* selected menu element */
#nav .current a, #nav li:hover > a {
    background:#7788aa url(../images/bg.png) repeat-x 0 -20px;
    color:#000;
    border-top:1px solid #f8f8f8;

    box-shadow:0 2px 2px rgba(0,0,0, .7); /*some css3*/
    -moz-box-shadow:0 2px 2px rgba(0,0,0, .7);
    -webkit-box-shadow:0 2px 2px rgba(0,0,0, .7);
    text-shadow:0 2px 2px rgba(255,255,255, 0.7);
}

/* sublevels */
#nav ul li:hover a, #nav li:hover li a {
    background:none;
    border:none;
    color:#000;
}
#nav ul li a:hover {
    background:#335599 url(../images/bg.png) repeat-x 0 -100px;
    color:#fff;

    border-radius:10px; /*some css3*/
    -moz-border-radius:10px;
    -webkit-border-radius:10px;
    text-shadow:0 2px 2px rgba(0,0,0, 0.7);
}

#nav ul li:first-child > a {
    -moz-border-radius-topleft:10px; /*some css3*/
    -moz-border-radius-topright:10px;
    -webkit-border-top-left-radius:10px;
    -webkit-border-top-right-radius:10px;
}
#nav ul li:last-child > a {
    -moz-border-radius-bottomleft:10px; /*some css3*/
    -moz-border-radius-bottomright:10px;
    -webkit-border-bottom-left-radius:10px;
    -webkit-border-bottom-right-radius:10px;
}

/* drop down */
#nav li:hover > ul {
    opacity:1;
    visibility:visible;
}
#nav ul {
    opacity:0;
    visibility:hidden;
    padding:0;
    width:175px;
    position:absolute;
    background:#aabbcc url(../images/bg.png) repeat-x 0 0;
    border:1px solid #7788aa;

    border-radius:10px; /*some css3*/
    -moz-border-radius:10px;
    -webkit-border-radius:10px;
    box-shadow:0 2px 2px rgba(0,0,0, .5);
    -moz-box-shadow:0 2px 2px rgba(0,0,0, .5);
    -webkit-box-shadow:0 2px 2px rgba(0,0,0, .5);

    -moz-transition:opacity .25s linear, visibility .1s linear .1s;
    -webkit-transition:opacity .25s linear, visibility .1s linear .1s;
    -o-transition:opacity .25s linear, visibility .1s linear .1s;
    transition:opacity .25s linear, visibility .1s linear .1s;
}
#nav ul li {
    float:none;
    margin:0;
}
#nav ul a {
    font-weight:normal;
    text-shadow:0 2px 2px rgba(255,255,255, 0.7);
}
#nav ul ul {
    left:160px;
    top:0px;
}