button {
 padding: 1rem 2rem;
 border: 0;
 box-shadow: 0px 0px 40px 0px red;
 font-weight: bolder;
 color: white;
 border-radius: 0.3rem;
 background-color: red;
 letter-spacing: .2rem;
}

button:hover {
 animation: changeBg 1s infinite;
 -webkit-animation-duration: 10s;
}

@keyframes changeBg {
 0%,
	100% {
  box-shadow: 0px 0px 40px 0px red;
 }

 25% {
  box-shadow: 0px 0px 40px 0px turquoise;
  background-color: turquoise;
 }

 50% {
  box-shadow: 0px 0px 40px 0px purple;
  background-color: purple;
 }

 75% {
  box-shadow: 0px 0px 40px 0px rgb(191, 204, 11);
  background-color: rgb(191, 204, 11);
 }
}