its element height. you can use line-separated divs as shown below.
<div class="row"> <div class="col-md-4 col-sm-6 col-xs-12">...</div> <div class="col-md-4 col-sm-6 col-xs-12">...</div> <div class="col-md-4 col-sm-6 col-xs-12">...</div> </div> <div class="row"> <div class="col-md-4 col-sm-6 col-xs-12">...</div> <div class="col-md-4 col-sm-6 col-xs-12">...</div> <div class="col-md-4 col-sm-6 col-xs-12">...</div> </div>
Tanbi source share