Generated by SassMeister.com.

input.scss

div.toc-wrapper {
  counter-reset: my-counter 0;

  $maxCount: 25;

  @for $counterValue from 1 through $maxCount {
    $formattedValue: if($counterValue < 10, '0' + $counterValue, $counterValue);

    li.toc-item-h2 {
      &:nth-child(#{$counterValue})::before {
        counter-increment: my-counter;
        content: '#{$formattedValue}:';
        padding-right: 8px;
      }
    }
  }
}

output.css

div.toc-wrapper {
  counter-reset: my-counter 0;
}
div.toc-wrapper li.toc-item-h2:nth-child(1)::before {
  counter-increment: my-counter;
  content: "01:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(2)::before {
  counter-increment: my-counter;
  content: "02:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(3)::before {
  counter-increment: my-counter;
  content: "03:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(4)::before {
  counter-increment: my-counter;
  content: "04:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(5)::before {
  counter-increment: my-counter;
  content: "05:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(6)::before {
  counter-increment: my-counter;
  content: "06:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(7)::before {
  counter-increment: my-counter;
  content: "07:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(8)::before {
  counter-increment: my-counter;
  content: "08:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(9)::before {
  counter-increment: my-counter;
  content: "09:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(10)::before {
  counter-increment: my-counter;
  content: "10:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(11)::before {
  counter-increment: my-counter;
  content: "11:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(12)::before {
  counter-increment: my-counter;
  content: "12:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(13)::before {
  counter-increment: my-counter;
  content: "13:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(14)::before {
  counter-increment: my-counter;
  content: "14:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(15)::before {
  counter-increment: my-counter;
  content: "15:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(16)::before {
  counter-increment: my-counter;
  content: "16:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(17)::before {
  counter-increment: my-counter;
  content: "17:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(18)::before {
  counter-increment: my-counter;
  content: "18:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(19)::before {
  counter-increment: my-counter;
  content: "19:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(20)::before {
  counter-increment: my-counter;
  content: "20:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(21)::before {
  counter-increment: my-counter;
  content: "21:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(22)::before {
  counter-increment: my-counter;
  content: "22:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(23)::before {
  counter-increment: my-counter;
  content: "23:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(24)::before {
  counter-increment: my-counter;
  content: "24:";
  padding-right: 8px;
}
div.toc-wrapper li.toc-item-h2:nth-child(25)::before {
  counter-increment: my-counter;
  content: "25:";
  padding-right: 8px;
}

settings.json

{
  "sass": {
    "compiler": "dart-sass/1.32.12",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}