Is there a css equivalent to 'align="center"'?

I tried:

margin-left: auto;
margin-right: auto;

But it doesn't center the elements in my table cells. I have a combination of text and <span> elements in the <td>s.

Once I set 'align="center"' in any of the <td> elements, it does center.

How do I achieve this in the stylesheet?

Btw, when I do text-align: center that works for text. But not for other elements like <span>s.

Edit:

The span has the following class, if that affects the alignment issue:

.dot {
    display: block;
    width: 10px;
    height: 10px;
    background: #333;
    -moz-border-radius: 5px;
    -webkit-border-radius: 5px;
    -khtml-border-radius: 5px;
}