button {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
  width: 130px;
  height: 45px;
  text-align: center;
  line-height: 45px;
  color: #fff;
  font-size: 15px;
  text-transform: uppercase;
  text-decoration: none;
  font-family: sans-serif;
  box-sizing: border-box;
  background: linear-gradient(90deg,#03a9f4,#ffeb3b,#f441af,#03a9f4);
  background-size: 400%;
  border-radius: 30px;
  z-index: 1;
  border: none;
  outline: none;
}

button:hover {
  animation: animate 6s linear infinite;
}

@keyframes animate {
  0% {
    background-position: 0%;
  }

  100% {
    background-position: 400%;
  }
}

button::before {
  content: '';
  position: absolute;
  top: -5px;
  left: -5px;
  right: -5px;
  bottom: -5px;
  z-index: -1;
  background: linear-gradient(90deg,#03a9f4,#ffeb3b,#f441af,#03a9f4);
  border-radius: 40px;
  filter: blur(20px);
  opacity: 0;
  transition: 0.5s;
}

button:hover::before {
  filter: blur(20px);
  opacity: 1;
  animation: animate 6s linear infinite;
}