SOURCE

<div class="outer-circle">
  <div class="inner-circle">  
  </div>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
</div>

@import url("https://fonts.googleapis.com/css?family=Montserrat&display=swap");

@import url("https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css");

body {
	font-family: "Montserrat", sans-serif;
	min-height: 100vh;
	display: flex;
	align-items: center;
	justify-content: center;
	flex-direction: column;
  background-color: #2A3137; 
}

* {
	font-family: "Montserrat", sans-serif !important;
  box-sizing: content-box;
}

.outer-circle {
  position: relative;
  height: 200px;
  width: 200px;
  background: linear-gradient(#14ffe9, #ffeb3b, #ff00e0);
  border-radius: 50%;
  animation: rotate 1.5s linear infinite;
}

.outer-circle span {
  position: absolute;
  height: 200px;
  width: 200px;
  background: linear-gradient(#14ffe9, #ffeb3b, #ff00e0);
  border-radius: 50%;
}

span:nth-child(1) {
  filter: blur(5px);
}

span:nth-child(2) {
  filter: blur(10px);
}

span:nth-child(3) {
  filter: blur(25px);
}

span:nth-child(4) {
  filter: blur(150px);
}

.inner-circle {
  height: 180px;
  width: 180px;
  position: absolute;
  background: black;
  top: 10px;
  left: 10px;
  border-radius: 50%;
  z-index: 9;
}

@keyframes rotate {
  0% {
    filter: hue-rotate(0deg);
  }
  100% {
    filter: hue-rotate(360deg);
  }
}