1. html

                  

                  <button class="btn btn-gradient">
                    Hover Me
                    </button>



                

2. css

                @import  url(https://fonts.googleapis.com/css?family=Lato);
body {
  display: flex;
  height: 100vh;
  justify-content: center;
  align-items: center;
  text-align: center;
  background: #222;
}

.btn {
  position: relative;
  padding: 1rem 3rem;
  font-family: Lato, sans-serif;
  font-size: 1.5rem;
  line-height: 1.5;
  color: black;
  text-decoration: none;
  background-color: white;
  border: transparent;
  outline: transparent;
  cursor: pointer;
  user-select: none;
  white-space: nowrap;
  animation: glow 8s linear infinite;
}
.btn-gradient {
  color: white;
  background: linear-gradient(90deg, #00dbde, #fc00ff, #00dbde);
  background-size: 300%;
  border-radius: 2em;
}
.btn-gradient::before {
  position: absolute;
  content: "";
  top: -5px;
  left: -5px;
  bottom: -5px;
  right: -5px;
  z-index: -1;
  background: inherit;
  background-size: inherit;
  border-radius: 4em;
  opacity: 0;
  transition: 0.5s;
}
.btn-gradient:hover::before {
  opacity: 1;
  filter: blur(20px);
  animation: glow 8s linear infinite;
}

@keyframes  glow {
  to {
    background-position: 300%;
  }
}