CSSだけで@keyframesを使用して多角形を回転させる方法のデモページ

.octagon {
  position: relative;
  width: 300px;
  height: 300px;
  margin: 50px auto;
}

.octagon-text {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  color: #fff;
  font-size: 20px;
  z-index: 1;
}

.octagon-list {
  height: 300px;
  animation: rotation 20s infinite linear;
}

.octagon-list li {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  width: 41.421356237%;
  height: 100%;
  margin: auto;
  background: #19243a;
}
.octagon-list li:nth-of-type(1) {
  transform: rotate(0deg);
}
.octagon-list li:nth-of-type(2) {
  transform: rotate(45deg);
}
.octagon-list li:nth-of-type(3) {
  transform: rotate(90deg);
}
.octagon-list li:nth-of-type(4) {
  transform: rotate(135deg);
}

@keyframes rotation {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}