三角形

.get-list{
  position: relative;
  100px;
  height: 50px;
  border-radius: 10px;
  background: olivedrab;
}
.get-list::before{
  position: absolute;
  top:-16px;
  left:40%;
  display: block;
  content:'';
  border- 10px;
  border-style: solid;
  border-color: transparent transparent #ff4d4d transparent;
}

　　

<div class="get-list"></div>