Creating a curved shadow with a color gradient

Here is a shadow that I am trying to replicate using just CSS and I just cannot work out how to do it. I have spent hours trying. I think I need to create 2 shadow elements but I'm not sure how to proceed.
The closest thing I get is with this (an abysmal attempt - I know):

.type-product:before, .type-product:after{
  z-index: -1;
  position: absolute;
  content: "";
  bottom: 25px;
  left: 21px;
  width: 50%;
  top: 80%;
  max-width:300px;
  background: #777;
  box-shadow: 0 35px 20px #777;
  transform: rotate(-8deg);
}
.type-product:after{
  transform: rotate(8deg);
  right: 20px;
  left: auto;
}

Most appreciative if any CSS gurus could provide any help.

NOTE: I don't think that this link covers my problem fully. It just discusses the curve - whilst I need a curve with a color-gradient...