.firework{
	position: fixed;
	z-index: 2;
}
.firework-element img{
	position: fixed;
	z-index: 0;
}

.firework-element img{
    animation: diminish 15s infinite ease-in-out;
}
@keyframes diminish {
  from {
    transform: scale(0);
    width: initial;
    z-index: 2;
  }
  to {
    transform: scale(1);
    width: 0;
    z-index: -1;
  }
}

.firework-element:first-child img {
   left: 1%;
   width: 20%;
}

.firework-element:nth-child(2) img {
   right: 10%;
   top: 10%;
   width: 30%;
}

.firework-element:nth-child(3) img {
   left: 20%;
   top: 20%;
   width: 50%;
}

.firework-element:last-child img {
   right:5%;
   width: 20%;
}