Continue Ordered List Numbering Automatically

I wonder how I can have the following ordered list in html 1 Item 1 1A Item 2 1B Item 3 2 Item 4 2A Item 5 2B Item 6 2C Item 7 3 Item 8

Solution 1:

Like this:

ol.number, .letter > ol {
  list-style-type: none;
}  

ol.number {
  counter-reset: number;
}

.letter > ol {
  counter-reset: letter;
}

ol.number > li:not(.letter):before {
  content: counter(number, decimal) " ";
  counter-increment: number;
}

.letter > ol > li:before {
  content: counter(number, decimal) counter(letter, upper-alpha) " ";
  counter-increment: letter;
}

<ol class="number">
  <li>Item 1</li>
  <li class="letter">
    <ol>
      <li>Item 2</li>
      <li>Item 3</li>
    </ol>
  </li>
  <li>Item 4</li>
  <li class="letter">
    <ol>
      <li>Item 5</li>
      <li>Item 6</li>
      <li>Item 7</li>
    </ol>
  </li>
  <li>Item 8</li>
</ol>

Or if you'd prefer to automate counting the index as well:

ol.number, .letter > ol {
  list-style-type: none;
}  

ol.number {
  counter-reset: number index;
}

.letter > ol {
  counter-reset: letter;
}

ol.number > li:not(.letter):before {
  content: counter(number, decimal) " ";
  counter-increment: number;
}

.letter > ol > li:before {
  content: counter(number, decimal) counter(letter, upper-alpha) " ";
  counter-increment: letter;
}

ol.number li:not(.letter):after {
  content: " " counter(index, decimal);
  counter-increment: index;
}

<ol class="number">
  <li>Item</li>
  <li class="letter">
    <ol>
      <li>Item</li>
      <li>Item</li>
    </ol>
  </li>
  <li>Item</li>
  <li class="letter">
    <ol>
      <li>Item</li>
      <li>Item</li>
      <li>Item</li>
    </ol>
  </li>
  <li>Item</li>
</ol>