<?xml version="1.0"?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        xmlns:html="http://www.w3.org/1999/xhtml">
<html:style><![CDATA[

window { -moz-box-align: start; -moz-box-pack: start }
hbox { background: yellow }
vbox { background: blue; width: 15px; height: 15px }

]]></html:style>

<hbox><vbox /><label value="a b c d e f" /></hbox>

</window>