CSS

css clip path alternative

/* 
one way of doing it by changing the border(left,right,top) width and color
in the ::after pseudo-element
demo:https://codepen.io/abdelghanymh/pen/mdqyaoR?editors=1100
*/

.indexBanner:after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 0;
  height: 0;
  
  /*this is where the magic happens*/
  border-left: 50vw solid white;
  border-right: 50vw solid white;
  border-top: 15vw solid transparent;
}
.indexBanner {
  background-image: url('http://nauci.se/Flipo/assets/images/study.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-position: center;
  background-size: cover;
  background-color: #404040;
  height: 500px;
  position: relative;
  overflow-x: hidden;
}
<div class="indexBanner"> 
</div> 

@https://stackoverflow.com/users/6263942/gleb-kemarsky