body {
  counter-reset: contador 100;
  animation: contar 30s forwards alternate infinite;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  
  &::after {
    content: counter(contador);
    font-size: 16em;
  }
  
}

@keyframes contar {
  @for $i from 100 through 1 {
    #{$i}% {
      counter-increment: contador #{-$i};
      background: hsl($i * 3.6,100,40);
      color: #fff;
    }
  }
}