<div class="circle"></div>
@keyframes fade-out-in {
    0% { opacity: 1; }
   50% { opacity: 0; }
  100% { opacity: 1; }
}

.circle {
  animation: 1s fade-out-in infinite;
}





.circle {
  margin: 50px auto;
  width: 80px;
  height: 80px;
  background: black;
  border-radius: 40px;
}

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