SO border box

HTML

<script src="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/css/bootstrap-combined.min.css">
<div class="container">
    <div class="row" >
        <div class="span12">
           <div class="row">
            <div class="span4"> 1 </div>
            <div class="span4"> 2 </div>
            <div class="span4"> 3 </div>
            </div><!-- end nested row -->
        </div><!-- end span 12 -->
        
</div> <!-- end row -->
</div><!-- end container -->

CSS

.span4{
    background-color:olive;
}

.span12{
    border:solid 8px black;
}