<div class="bg">
  <div class="test"></div>
</div>

$mainColor:#B1ECC6;
$bgColor:#fff;
.bg{
  background:$mainColor;  
  height:50vh;
  width:100vw;
  position:relative;
  &:after{
    position:absolute;
    top:100%;
    left:0;
    content:'';
    height:0;
    width:0;
    border-right:100vw solid $mainColor;
    border-bottom:10vw solid transparent;
    border-top:0px solid transparent;
    overflow:hidden;
  }
}