I cannot get the same height for a columns with different contents.
<div class="row row-flex row-flex-wrap">
<div class="col-sm-6 col-md-3">
<div class="thumbnail">
<img class="img-responsive center-block" src="img/tabano.jpg" alt="..." data-src="holder.js/242x200/auto">
<div class="caption">
<h3>Tábano</h3>
<p>Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit.</p>
<p>
<a href="index.html" class="btn btn-primary" role="button">Button</a>
<a href="#" class="btn btn-default" role="button">Button</a>
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-md-3">
<div class="thumbnail">
<img class="img-responsive center-block" src="img/tabano.jpg" alt="..." data-src="holder.js/242x200/auto">
<div class="caption">
<h3>Tábano</h3>
<p>Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit.</p>
<p>
<a href="index.html" class="btn btn-primary" role="button">Button</a>
<a href="#" class="btn btn-default" role="button">Button</a>
</p>
</div>
</div>
</div>
1st content is longer than 2nd, but columns take different height, even with row-flex.