収縮ボタン

↓HTML

<div class="pushBtn">
  PUSH
</div>

↓CSS

.pushBtn {
    border: 0.5px solid
    border-radius: 5px;
    margin: 0 auto;
    width: 33%;
    text-align: center;
    animation: pushBtn 2s ease-out infinite;
    animation-direction: alternate;
    opacity: 1;
  }
@keyframes pushBtn {
  0%, 40%, 60%, 80% {
    transform: scale(1.0);
  }
  50%, 70% {
    transform: scale(0.95);
  }
}