<!DOCTYPE html>
<html>
  <style>
    div { height: 20px; }
    div > div { width: 100px; background: green; }
    body > div { direction: ltr }
  </style>
  <body style="width: 400px">
    <div><div style="margin-left: 100px; margin-right: auto"></div></div>
    <div><div style="margin-left: auto; margin-right: 100px"></div></div>
    <div><div style="margin-left: auto; margin-right: auto"></div></div>
    <div><div style="margin-left: 200px; margin-right: auto"></div></div>
    <div><div style="margin-left: 100px; margin-right: 100px"></div></div>
  </body>
</html>