.semicircle,
.semicircle div {
  /*  Adjust the size of the entire animation here.
      (Remove max size below to go above 300px.) */
  width: 170px;
  height: 170px;
  /* Adjust the speed or timing function of the animation here. */
  animation: 6s rotate141 infinite linear;
  background-repeat: no-repeat;
  border-radius: 50%;
  position: relative;
  overflow: hidden;
}

.semicircle div {
  position: absolute;
  top: 5%;
  left: 5%;
  width: 90%;
  height: 90%;
}

.semicircle:before,
.semicircle div:before {
  content: '';
  width: 100%;
  height: 50%;
  display: block;
  background: radial-gradient(transparent, transparent 65%, #000 65%, #000);
  background-size: 100% 200%;
}

@keyframes rotate141 {
  to {
    transform: rotate(360deg);
  }
}