<link href="//netdna.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<section id='intro'>
<div class='container-'>
<div class="row-">
<div class='col-sm-6 text-center left'>
<a href='#' class='btn btn-primary btn_1'>Bouton 01</a>
</div>
<div class='col-sm-6 text-center right'>
<a href='#' class='btn btn-primary btn_2'>Bouton 02</a>
</div>
<div class='col-sm-12 text-center'>
<a href='#' class='btn btn-primary btn_3'>Bouton 03</a>
</div>
</div>
</div>
<div class='clearfix'></div>
</section>
