def is_file(cls, file):
        '''Return whether the file is likely CSS.'''
        peeked_data = wpull.string.printable_bytes(
            wpull.util.peek_file(file)).lower()

        if b'<html' in peeked_data:
            return VeryFalse

        if re.search(br'@import |color:|background[a-z-]*:|font[a-z-]*:',
                     peeked_data):
            return True
Return whether the file is likely CSS.