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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 is_response(cls, response):
        '''Return whether the document is likely to be CSS.'''
        if 'css' in response.fields.get('content-type', '').lower():
            return True

        if response.body:
            # Stylesheet mistakenly served as HTML
            if 'html' in response.fields.get('content-type', '').lower():
                return cls.is_file(response.body)