How to horizontally center an unordered list of unknown width?

Question

It is common to have a set of links in a footer represented in a list, such as:

<div id="footer">
    <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">About</a></li>
        <li><a href="#">Contact</a></li>
    </ul>
</div>

I want everything inside div#footer to be centered horizontally. If it was a paragraph, you would just easily say: p { text-align: center; }. Or if I knew the width of the <ul> I could just say #footer ul { width: 400px; margin: 0 auto; }.

But how do you center the unordered list items without setting a fixed width on the <ul>?

EDIT: clarification - the list items should be next to each other, not below.

Answer 1

The solution, if your list items can be display: inline is quite easy:

#footer { text-align: center; }
#footer ul { list-style: none; }
#footer ul li { display: inline; }

However, many times you must use display:block on your <li>s. The following CSS will work, in this case:

#footer { width: 100%; overflow: hidden; }
#footer ul { list-style: none; position: relative; float: left; display: block; left: 50%; }
#footer ul li { position: relative; float: left; display: block; right: 50%; }