<ol>
  <li>first item</li>
  <li>second item
    <ol>
      <li>second item first subitem</li>
      <li>second item second subitem</li>
      <li>second item third subitem</li>
    </ol>
  </li>
  <li>third item</li>
</ol>
@import url('https://fonts.googleapis.com/css?family=Lato:400,700');

body {
  font-size: 18px;
  font-family: 'Lato', sans-serif;
}

ol {
  counter-reset: li; 
  list-style: none; 
}

li {
  line-height: 1.8;
}

ol > li::before {
  margin-right: 0.25rem;
  content:counter(li) ".";
  counter-increment: li;
  font-weight: bold;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.