JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css">
<div class="row">
   <div class="span5">span5</div>
   <div class="span3">span3</div>
   <div class="span2">
      <div class="row-fluid">
         <div class="span12">span2</div>
         <div class="span12">span2</div>
      </div>
   </div>
   <div class="span2">span2</div>
</div>
<div class="row">
   <div class="span6">
      <div class="row-fluid">
         <div class="span12">span6</div>
         <div class="span12">span6</div>
      </div>
   </div>
   <div class="span6">span6</div>
</div>

CSS

[class*="span"] {
    border: 1px solid black;
}

.row-fluid [class*="span"] {
    margin-left: 0;
}