/**
  核心在于引导线旋转功能的实现，小球是在引导线的基础上定位的。
*/
body {
  margin: 0;
  padding: 0;
}

.circle {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 400px;
  height: 400px;
  background-color: transparent;
  border-radius: 50%;
  border: 2px solid #262626;
}

.line {
  position: absolute;
  top: 50%;
  width: calc(50% - 1px);
  height: 2px;
  background-color: #262626;
  animation: animate 5s linear infinite;
  transform-origin: right;
}

@keyframes animate {
  from {
    transform: rotate(0);
  }
  to {
    transform: rotate(360deg);
  }
}

.line::before {
  content: '';
  display: block;

  position: absolute;
  top: -20px;
  left: -11px;

  width: 20px;
  height: 20px;
  background-color: orangered;
  border-radius: 50%;
}

.line::after {
  content: '';
  display: block;

  position: absolute;
  /* top为0，会使圆心球动 */
  top: 0px;
  right: -11px;

  width: 20px;
  height: 20px;
  background-color: orangered;
  border-radius: 50%;
}