如何居中UL

Question

I'm trying to get a ul horizontally centered within the space but no matter what I try it remains left aligned.

<nav>
    <div id="home">
    <ul id="topnav">
        <li class="home"><a href="#">home</a></li>
        <li class="products"><a href="#">products</a></li>
        <li class="support"><a href="#">support</a></li>
        <li class="wtb"><a href="#">where to buy</a></li>
        <li class="webstore"><a href="#" target="_blank">web store</a></li>
        <li class="contact"><a href="#">contact us</a></li>
        <li class="facebook"><a href="#" target="_blank"
            title="Hauppauge Computer Works">facebook</a></li>
    </ul>
    </div>
</nav>

CSS: CSS file here

Answer 1

ul#topnav {
    padding: 0px;
    list-style: none;
    margin-right: auto;
    margin-left: auto;
    margin-top: 0px;
    margin-bottom: 0px;
    position: relative;
    left: auto;
        width: 123px;
}