<ol>
  <li>Item One</li>
  <li>Item Two
  <ol>
    <li>Sub-item One
      <ol><li>Sub-sub-item One</li>
        <li>Sub-sub-item Two</li>
      </ol>
      </li>
    <li>Sub-item Two</li>
    </ol>
  </li>
  <li>Item Three</li>
</ol>

::marker {
  content: counters(list-item,'.') ':';
  color: #00b7a8;
  font-weight: bold;
}

li {
  padding-left: .5em;
}

li li {
  counter-reset;
}

body {
  font: 1.4em/1.3 "Gill Sans", "Gill Sans MT", Calibri, sans-serif;
  margin: 2em 3em;
}