<ul>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
  <li>Lorem ipsum dolor sit amet.</li>
</ul>

ul {
  list-style: none;
  counter-reset: my-counter;
  margin: 0;
  padding: 0;
}
ul li {
  counter-increment: my-counter;
  padding: 5px 0;
}
ul li::before {
  content: "0" counter(my-counter);
  margin-right: 15px;
}
ul li:nth-child(1n + 10)::before {
  content: counter(my-counter);
}