<a class="blink" href="#">button</a>

body {
  min-height: 100vh;
  margin: 0;
  padding: 10px;
  display: flex;
  justify-content: center;
  align-items: center;
}
a {
  font-weight: 600;
  color: #fff;
  background: #5876a3;
  padding: 10px 20px;
  border-radius: 5px;
  text-decoration: none;
  box-shadow: 0 4px 0 #3f5c88;
}


.blink {
  -webkit-animation: blink 1s ease-in-out infinite alternate;
  animation: blink 1s ease-in-out infinite alternate;
}
@-webkit-keyframes blink {
  0% {opacity: 0;}
  100% {opacity: 1;}
}
@keyframes blink {
  0% {opacity: 0;}
  100% {opacity: 1;}
}