def parse_css(self, css):
        """
        Parse a css style sheet into the CSS object.

        For the moment this will only work for very simple css
        documents.  It works by using regular expression matching css
        syntax.  This is not bullet proof.
        """
        rulesets = self.ruleset_re.findall(css)
        for (selector, declarations) in rulesets:
            rule = Rule(self.parse_selector(selector))
            rule.properties = self.parse_declarations(declarations)
            self.rules.append(rule)
Parse a css style sheet into the CSS object.

        For the moment this will only work for very simple css
        documents.  It works by using regular expression matching css
        syntax.  This is not bullet proof.