/* HTML */
<a href="#"><button class="button-08">HOVER ME</button></a>

/* CSS */
.button-08 {
 text-decoration: none; 
 border: none;
 font-size: 14px;
 font-family: inherit;
 color: #fff;
 width: 9em;
 height: 3em;
 line-height: 2em;
 text-align: center;
 background: linear-gradient(90deg,#03a9f4,#f441a5,#ffeb3b,#03a9f4);
 background-size: 300%;
 border-radius: 30px;
 z-index: 1;
}

.button-08:hover {
 animation: ani 8s linear infinite;
 border: none;
}

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

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

.button-08:before {
 content: '';
 position: absolute;
 top: -5px;
 left: -5px;
 right: -5px;
 bottom: -5px;
 z-index: -1;
 background: linear-gradient(90deg,#03a9f4,#f441a5,#ffeb3b,#03a9f4);
 background-size: 400%;
 border-radius: 35px;
 transition: 1s;
}

.button-08:hover::before {
 filter: blur(20px);
}

.button-08:active {
 background: linear-gradient(32deg,#03a9f4,#f441a5,#ffeb3b,#03a9f4);
}