body {
  background-color: black;
}

html, body {
  overflow:hidden;
}

.vignetting {
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: -1;
  position: absolute;
  margin: auto;
}

.vignetting:after {
  content: "";
  display: flex;
  border-radius: 0%;
  position: absolute;
  top:0;
  bottom: 0;
  left: 0;
  right: 0;
  box-shadow:
    inset -10px 10px 40px 0px black, 
    inset -10px -10px 40px 0px black, 
    inset 10px -10px 40px 0px black, 
    inset -10px 10px 40px 0px black;
}