<div>select file</div>

div {
  padding: .5em 1.5em;
  border: 2px solid #999;
  display: inline-block;
  position: relative;
  font-family: sans;
}
div::after {
  content: '';
  background: #fff;
  position: absolute;
  bottom: -0px;
  right: -7px;
  transform: rotate(45deg);
  transform-origin: 0 100%;
  border-left: 2px solid #999;
  width: 15px;
  height: 15px;
  z-index: 10;
}