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

.firework-element img{
    animation: diminish 10s infinite ease-in-out;
}

@keyframes diminish {
  from {
    transform: scale(0);
    width: initial;
    z-index: 2;
  }
  to {
    transform: scale(3);
    width: 0;
    z-index: -1;
  }
}


.firework-element:first-child img {
   left: 1%;
   width: 70%;
}

.firework-element:nth-child(2) img {
   right: 10%;
   top: 10%;
   width: 80%;
}

.firework-element:nth-child(3) img {
   left: 20%;
   top: 20%;
   /*width: 100%;*/
   animation-delay: 8s;
}

.firework-element:nth-child(4) img {
   left: 50%;
   top: 50%;
   /*width: 100%;*/
   animation-delay: 8s;
}

.firework-element:nth-child(5) img {
   left: 40%;
   top: 40%;
   /*width: 100%;*/
   animation-delay: 8s;
}

.firework-element:last-child img {
   right:5%;
   width: 70%;
}

@media (max-width: 991px) {

  @keyframes diminish {
    from {
      transform: scale(0);
      width: initial;
      z-index: 2;
    }
    to {
      transform: scale(1);
      width: 0;
      z-index: -1;
    }
  }

  .firework-element:nth-child(4) img {
     display: none;
     width: 0%;
  }

  .firework-element:nth-child(5) img {
     display: none;
     width: 0%;
  }
}