@supports (animation-timeline: view(-50vh)){
  .slide-timeline:not(:last-child) .slide-timeline-left,
  .slide-timeline:not(:last-child) .slide-timeline-right {
    opacity: 0.3;
    animation: scroll-reveal;
    animation-timeline: view(-50vh);
    animation-range: cover 0px;
  }  
}

@keyframes scroll-reveal{
  0%{
    opacity: 0.3;
  }
  
  50% {
    opacity: 1;
  }
  
  100% {
    opacity: 0.3;
  }
}