Can I style numbering an ordered list that has a start attribute value?

Question

Here's the problem:

I have an ol li ordered list with a start attribute like so:

    .custom {
      margin: 0;
      padding: 0;
      list-style-type: none;
    }
    
    .custom li {
      counter-increment: step-counter;
      margin-bottom: 10px;
    }
    
    .custom li::before {
      content: counter(step-counter);
      margin-right: 5px;
      font-size: 80%;
      background-color: rgb(0,200,200);
      color: white;
      font-weight: bold;
      padding: 3px 8px;
      border-radius: 3px;
    }

    <ol start="6" class="custom">
      <li>This is the sixth item</li>
      <li>This is the seventh item</li>
      <li>This is the eighth item</li>
      <li>This is the ninth item</li>
      <li>This is the tenth item</li>
    </ol>

I get the following output on the browser:

Is it possible to serialize the list-style numbering on an ordered list using the value in start attribute instead of 1? No JavaScript can be used for this though.

Answer 1

You can simulate this using CSS variable that you set instead of start and use it to reset the counter. For semantic purpose you can also keep start attribute.

.custom {
  margin: 0;
  padding: 0;
  list-style-type: none;
  counter-reset: step-counter calc(var(--start) - 1);
}

.custom li {
  counter-increment: step-counter;
  margin-bottom: 10px;
}

.custom li::before {
  content: counter(step-counter);
  margin-right: 5px;
  font-size: 80%;
  background-color: rgb(0, 200, 200);
  color: white;
  font-weight: bold;
  padding: 3px 8px;
  border-radius: 3px;
}

<ol style="--start:6" start="6" class="custom">
  <li>This is the sixth item</li>
  <li>This is the seventh item</li>
  <li>This is the eighth item</li>
  <li>This is the ninth item</li>
  <li>This is the tenth item</li>
</ol>

Answer 2

li tag have no access to parent attribute.

This is the best way i saw, using content: attr()

    .custom {
      margin: 0;
      padding: 0;
      list-style-type: none;
    }
    
    .custom li {
      counter-increment: step-counter;
      margin-bottom: 10px;
    }
    
    .custom li::before {
      content: attr(data-idx);
      margin-right: 5px;
      font-size: 80%;
      background-color: rgb(0,200,200);
      color: white;
      font-weight: bold;
      padding: 3px 8px;
      border-radius: 3px;
    }

    <ol class="custom">
      <li data-idx="6">This is the sixth item</li>
      <li data-idx="7">This is the seventh item</li>
      <li data-idx="8">This is the eighth item</li>
      <li data-idx="9">This is the ninth item</li>
      <li data-idx="10">This is the tenth item</li>
    </ol>