arrowcode

.box {
  width: 150px;
  height: 75px;
  background-color: black;
  color: #fff;
  padding: 20px;
  position: relative;
  margin: 40px;
  float: left;
}

.box.arrow-left:after {
  content: " ";
  position: absolute;
  left: -15px;
  top: 0px;
  border-top: 15px solid transparent;
  border-right: 15px solid black;
  border-left: none;
  border-bottom: 15px solid transparent;
}