Flexbox Thumbnail Cards Responsive Equal Height Boxes for Twitter Bootstrap 3

<div class="flex-row row">
<div class="col-xs-6 col-sm-4 col-lg-3">
</div>
</div>

@media only screen and (min-width : 481px) {
   .flex-row.row {
  display: flex;
  flex-wrap: wrap;
   }
   .flex-row.row > [class*='col-'] {
  display: flex;
  flex-direction: column;
   }
  .flex-row.row:after, 
  .flex-row.row:before {
  display: flex;
  }
}

<div class="thumbnail">
  <div class="caption">
    <h3>Title</h3>
    <p class="flex-text"> Content ...<p>
    <p><a class="btn btn-primary" href="#">Link</a></p>
  </div>
</div>

.flex-row .thumbnail,
.flex-row .caption {
  flex:1 0 auto;
  flex-direction:column;
}
.flex-text {
  flex-grow:1
}
.flex-row img {
  height:auto;
  width:100%
}