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

* {
  box-sizing: border-box;
}
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 {
  position: relative;
  overflow: hidden;
}
.blink::before {
  content: "";
  width: 20px;
  height: 100%;
  background: rgba(255,255,255,.8);
  position: absolute;
  top: -100px;
  left: 0;
  opacity: 0;
  -webkit-transform: rotate(45deg);
  transform: rotate(45deg);
  -webkit-animation: blink 2s ease-in-out infinite;
  animation: blink 2s ease-in-out infinite;
}
@-webkit-keyframes blink {
  0% {
    -webkit-transform: scale(0) rotate(45deg);
    transform: scale(0) rotate(45deg);
    opacity: 0;
  }
  80% {
    -webkit-transform: scale(0) rotate(45deg);
    transform: scale(0) rotate(45deg);
    opacity: .5;
  }
  81% {
    -webkit-transform: scale(4) rotate(45deg);
    transform: scale(4) rotate(45deg);
    opacity: 1;
  }
  100% {
    -webkit-transform: scale(50) rotate(45deg);
    transform: scale(50) rotate(45deg);
    opacity: 0;
  }
}
@keyframes blink {
  0% {
    -webkit-transform: scale(0) rotate(45deg);
    transform: scale(0) rotate(45deg);
    opacity: 0;
  }
  80% {
    -webkit-transform: scale(0) rotate(45deg);
    transform: scale(0) rotate(45deg);
    opacity: .5;
  }
  81% {
    -webkit-transform: scale(4) rotate(45deg);
    transform: scale(4) rotate(45deg);
    opacity: 1;
  }
  100% {
    -webkit-transform: scale(50) rotate(45deg);
    transform: scale(50) rotate(45deg);
    opacity: 0;
  }
}