background-ref.xhtml

<?xml version="1.0"?>
<?xml-stylesheet href="style.css" type="text/css"?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        xmlns:html="http://www.w3.org/1999/xhtml">
  <html:style>
    window {
      background-color: blue;
    }
  </html:style>

  <vbox>
    <html:div class='file'>
      <html:button>Browse&#8230;</html:button><label value="No file selected."/>
    </html:div>
  </vbox>
</window>