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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_css_files(cls, extra_files):
 """Return all CSS files from the Media class. Args: extra_files (dict):
 The contents of the Media class's original :py:attr:`css` attribute, if one was provided. Returns: dict: The CSS media types and files to return for the :py:attr:`css` attribute. """

        packager = Packager()
        css_packages = getattr(cls, 'css_packages', {})

        return dict(
            (media_target,
             cls._get_media_files(packager=packager,
                                  media_packages=media_packages,
                                  media_type='css',
                                  extra_files=extra_files.get(media_target,
                                                              [])))
            for media_target, media_packages in six.iteritems(css_packages)
        )