For lists to be displayed correctly, the list items need to be inside the <ol> and </ol> tags.

Order the lines to put the list item in its proper place.

<html>
 <body>
  <ol>
   <li>Tortoise</li>
  </ol>
 </body>
</html>]]>

Make sure the list item, <li>Tortoise</li>, is between <ol> and </ol>.