fronMood

<div class="container">
</div>

.container{
  width: 200px;
  height: 200px;
  background-color: red;
  position: relative;
}
.container:after{
  content:"";
  position: absolute;
  top: 45%;
  left: 0px;
  transform: translateX(-20%);
  transform: rotate(-90deg);
  border:15px solid;
  border-color: #fff transparent transparent transparent;
}

.container:before{
  content:"";
  position: absolute;
  top: 45%;
  right: 0px;
  transform: translateX(-20%);
  transform: rotate(90deg);
  border:15px solid;
  border-color: #fff transparent transparent transparent;
}