title: Bootstrap span inside a span
body: <p>I have some difficulties to understand how put span inside span with bootstrap.</p>
  
  <p>I want to have one block centered, with inside : </p>
  
  <p>-One row with inside :<br>
      -One block at left (span6)
      -One block at right (span6)</p>
  
  <p>-One row with inside : 
      -One button centered (span 6 offset3)</p>
  
  <p>You could see the problem here : 
  <a href="http://jsfiddle.net/UBTv4/18/" rel="nofollow noreferrer">http://jsfiddle.net/UBTv4/18/</a></p>
  
  <pre><code>&lt;div class='row'&gt;
  &lt;div class='span6 offset3'&gt;
      &lt;div class='well'&gt;
          &lt;h2&gt;Title&lt;/h2&gt;      
              &lt;div class='row'&gt;
                  &lt;div class='span6'&gt;
                      &lt;p class="lead"&gt;Bloc left : &lt;/p&gt;
                  &lt;/div&gt;              
                  &lt;div class='span6'&gt;
                      &lt;p class="lead"&gt;Bloc right : &lt;/p&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
              &lt;div class='row'&gt;
                  &lt;div class='span6 offset3'&gt;
                      &lt;input id="play" type="submit" value="play" class="btn btn-primary"/&gt;       
                  &lt;/div&gt;
              &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p></p>
  
  <p>What is the problem ?</p>
  
  <p>I want something like that : </p>
  
  <p><img src="https://i.stack.imgur.com/2lxeR.png" alt="enter image description here"></p>