index.scss

$input: 1234321 !default;

%isPalindrome {
  content: 'Yep! That\'s a palindrome';
}

%notPalindrome {
  content: 'Nope, not a palindrome';
}

@function isPalindrome($var) {
  $local: $var;
  $compareArray: ();

  @while ($local > 0) {
    $remainder: $local % 10;
    $local: round($local / 10);

    $compareArray: append($compareArray, $remainder);
  }

  $length: length($compareArray);

  @for $i from 1 through $length {
    $inverse: 1 + $length - $i;
    @if (nth($compareArray, $i) != nth($compareArray, $inverse)) {
      @return false;
    }
  }

  @return true;
}

.input-#{$input} {
  @if isPalindrome($input) {
    @extend %isPalindrome;
  } @else {
    @extend %notPalindrome;
  }
}