div {
  width: 10rem;
  height: 10rem;
  margin: 3rem auto;
  animation: myAnimation 5s infinite;
}

@keyframes myAnimation {
  
  from {
    transform: scale(0.5);
    background: red;
  }
  
  to {
    transform: scale(1);
    background: blue;
  }
  
}