SOURCE

<span class="arrow">
  <span class="out">
  </span>
  <span class="inner">
  </span>
</span>

.arrow {
  display: inline-block;
  width: 30px;
  height: 30px;
  position: relative;
  overflow: hidden;
  background: #ffffff;
}

.out {
  display: inline-block;
  width: 20px;
  height: 30px;
  border-left: 20px solid #4189ff;
  border-top: 15px dashed transparent;
  border-bottom: 15px dashed transparent;
  border-right: 20px;
  box-sizing: border-box;
}

.inner {
  position: absolute;
  top: 0;
  left: -3px;
  display: inline-block;
  width: 20px;
  height: 30px;
  border-left: 20px solid #ffffff;;
  border-top: 15px dashed transparent;
  border-bottom: 15px dashed transparent;
  border-right: 20px;
  box-sizing: border-box;
}