Это CSS — то что мы ранее называли таблица стилей:

function isPrime($n, $primesList) {
  @each $prime in $primesList {
    @if ($n % $prime == 0) {
      @return false;
    }
  }
  @return true;
}

@mixin primeCounter($selector, $upperBound: 2000) {
  
  $curr: 2;
  $primesList: [];
  
  @while $curr <= $upperBound {
    @if isPrime($curr, $primesList) {
      $primesList: append($primesList, $curr);
    }
    $curr: $curr + 1;
  }
  :root {
    @each $prime in $primesList {
        --p#{$prime}: 1;
    }
  }
  $mult: "1";
  @each $prime in $primesList {
    $mult: $mult " * var(--p#{$prime})";
    $val: $prime;
    @while $val <= $upperBound {
      #{$selector}:nth-child(#{$val}n) {
        --p#{$prime}: #{$val};
      }
      $val: $val * $prime;
    }
  }
  
  #{$selector} {
    --n: calc(#{$mult});
  }
}

Тут: https://habr.com/ru/companies/qiwi/articles/765596/