css/css-backgrounds/reference/background-size-044-ref.html

<!DOCTYPE html>

  <title>CSS Reftest Reference</title>

  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">

  <style>
  div#black-border
    {
      border: black solid 40px;
      height: 400px;
      width: 400px;
    }

  div#inner-orange
    {
      background-color: orange;
      border-left: blue solid 16px;
      border-right: blue solid 16px;
      height: 100%;
      margin: 0px auto;
      /* the orange block is horizontally centered inside div#black-border */
      width: 208px; /* [(40 + 400 + 40) / 2 ] - 32 == 208px */
    }
  </style>

  <div id="black-border"><div id="inner-orange"></div></div>