button {
  background: linear-gradient(-45deg, #3f00b5, #9f69fe, #27c8b7, #3f00b5);
  background-size: 800% 400%;
  padding: 1em 2em;
  display: inline-block;
  border: none;
  border-radius: 10px;
  font-size: 17px;
  font-weight: 700;
  color: white;
  transition: all .5s ease-in-out;
  animation: gradient 10s infinite cubic-bezier(.62, .28, .23, .99) both;
}

button:hover {
  animation: gradient 3s infinite;
  transform: scale(1.05);
}

button:active {
  animation: gradient 3s infinite;
  transform: scale(0.8);
}

@keyframes gradient {
  0% {
    background-position: 0% 50%;
  }

  50% {
    background-position: 100% 50%;
  }

  100% {
    background-position: 0% 50%;
  }
}