<div class="row">
          <div class="col-xs-12 col-sm-6 col-md-8">.col-xs-12 .col-sm-6 .col-md-8</div>
          <div class="col-xs-6 col-md-4">.col-xs-6 .col-md-4</div>
        </div>
        <div class="row">
          <div class="col-xs-6 col-sm-4">.col-xs-6 .col-sm-4</div>
          <div class="col-xs-6 col-sm-4">.col-xs-6 .col-sm-4</div>
          <!-- Optional: clear the XS cols if their content doesn't match in height -->
          <div class="clearfix visible-xs-block"></div>
          <div class="col-xs-6 col-sm-4">.col-xs-6 .col-sm-4</div>
        </div>