<rules
    xmlns="http://namespaces.plone.org/diazo"
    xmlns:css="http://namespaces.plone.org/diazo/css"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <theme href="theme.html" />

    <replace css:theme="#content" css:content="#content" if="$someparam = 'value1'" />

</rules>
