*,
*:before,
*:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
.box {
  position: absolute;
  top: -4em;
  left: 0;
  height: 46em;
  width: 40em;
  margin: auto;
  overflow: hidden;
}
.wrapper {
  position: relative;
  height: 38em;
  width: 38em;
  margin: 1em auto;
  overflow: hidden;
  background: white;
}
.cross {
  position: absolute;
  top: 0;
  left: 0;
  background: #333;
  height: 6em;
  width: 2em;
  margin: 0;
  animation: rot 3s ease-in-out infinite;
  @for $i from 0 to 10 {
    &.r#{$i}
    {
      @for $j from 0 to 9 {
        &.c#{$j}
        {
          top: 6em * $i + 2em * $j - 9;
          left: -2em * $i + 6em * $j;
        }
      }
    }
  }
  &:before {
    content: '';
    height: 2em;
    width: 6em;
    margin: -1em 0;
    position: absolute;
    top: 33.333%;
    left: -100%;
    margin: 0;
    background: inherit;
  }
}
.white {
  top: -8em;
  left: -2em;
  background: #333;
  opacity: 0;
  animation: show 3s linear infinite;
  .cross {
    background: #fff;
    animation-direction: reverse;
  }
}
@keyframes rot {
  50% {
    transform: rotate(-90deg);
  }
  100% {
    transform: rotate(-90deg);
  }
}
@keyframes show {
  0%,
  50% {
    opacity: 0;
  }
  50.1%,
  100% {
    opacity: 1;
  }
}