<div class="gradient"></div>

.gradient {
  width: 200px;
  height: 200px;

  background: linear-gradient(
    #03001e 0%, #03001e 25%,
    #7303c0 25%, #7303c0 50%, 
    #ec38bc 50%, #ec38bc 75%,
    #fbc6ec 75%, #fbc6ec 100%
  );
}