Edit in JSFiddle


              
<div class="comment">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iure voluptate eum.</div>
.comment{
  max-width:80%;
  margin:30px;
  background:#f03;
  font:14px/1.5 arial,verdana,tahoma;
  color:#fff;
  padding:20px;
  box-sizing:border-box;
  border-radius:4px;
  position:relative;
  &:after{
    content:'';
    display:block;
    width:20px;
    height:15px;
    background:#f03;
    position:absolute;
    left:3px;
    bottom:-5px;
    transform:rotate(-30deg);
  }
}