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:

Answer 1

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;
    }

    

      
This is the sixth item
      
This is the seventh item
      
This is the eighth item
      
This is the ninth item
      
This is the tenth item