<div></div>

body {
  margin: 0;
  background-color: #000;
}

div {
  position: absolute;
  top: calc(50% - 20px);
  left: calc(50% - 20px);
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: #fff;
  box-shadow:
    0 0 60px 30px #fff,
    0 0 100px 60px #f0f,
    0 0 140px 90px #0ff;
}