css - How do I center a Bootstrap div with a 'spanX' class?

Question

I use bootstrap and am trying to center a div(span7) like that:

<div class="row-fluid">
    <div id="main" class="span7">
        Lorem ipsum dolor sit amet
    </div>
</div>

my css code is:

#main{
    margin:0px auto;
}

But it isn't set at the center. How can i set center?

EDIT

span7 is now col-7 in Bootstrap 4 and row-fluid is deprecated(Instead of this, use container-fluid and row).

Answer 1

Twitter's bootstrap .span classes are floated to the left so they won't center by usual means. So, if you want it to center your span simply add float:none to your #main rule.

CSS

#main {
 margin:0 auto;
 float:none;
}