<!DOCTYPE html>
<html>
<head>
<style>
.hitregion {
  width: 100px;
  height: 100px;
  background-color: green;
}
.hitregion:after {
  content: "";
  border: 40px solid;
  outline: 10px solid;
  position: absolute;
  width: 0;
  height: 0;
  margin-left: 140px;
  margin-top: 10px;
  color: green;
}
</style>
</head>
<body>
<div class="hitregion"></div>
</body>
</html>