.rotated_gradient_box {
  filter: hue-rotate(360deg);
  width: 200px;
  height: 100px;
  border-radius: 21px;
  border: 10px solid transparent;
  background-image: linear-gradient(#444, #444), linear-gradient(to left,#37a9fa,#5951f3);
  background-clip: content-box, border-box;
  background-origin: border-box;
  animation: huerotate 6s infinite linear;
}

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