How to use the diazo.cssrules.convert_css_selectors function in diazo

parser = etree.HTMLParser()
    if xinclude:
        # XXX: read_network limitation not yet supported  # NOQA: T000
        #   for xinclude
        rules_doc.xinclude()
    if stop == 1:
        return rules_doc
    rules_doc = add_identifiers(rules_doc)
    if stop == 2 or stop == 'add_identifiers':
        return rules_doc
    if update:
        rules_doc = update_namespace(rules_doc)
    if stop == 3:
        return rules_doc
    if css:
        rules_doc = convert_css_selectors(rules_doc)
    if stop == 4:
        return rules_doc
    rules_doc = fixup_theme_comment_selectors(rules_doc)
    if stop == 5:
        return rules_doc
    rules_doc = expand_themes(rules_doc, parser, absolute_prefix, read_network)
    if theme is not None:
        rules_doc = add_theme(
            rules_doc,
            theme,
            parser,
            absolute_prefix,
            read_network,
        )
    if stop == 6:
        return rules_doc