<ol>
  <li>First</li>
  <li>Second</li>
  <li>Third</li>
</ol>

ol {
  counter-reset: indents -1 numbers 0;
}
li {
  counter-increment: indents 1 numbers 1;
  list-style-position: inside;
}
li:first-child::marker {
  content: '1. ';
}
li::marker {
  content: counter(indents, symbols(symbolic "----")) ' ' counter(numbers) '. ';
}