self.block_type = block_type
    self.layers = layers
    self.num_classes = num_classes
    self.input_channels = input_channels
    self.cardinality = cardinality
    self.base_width = base_width
    self.stem_width = stem_width
    self.stem_type = stem_type
    self.avg_down = avg_down
    super().__init__(**kwargs)

The three important things to remember when writing you own configuration are the following:
- you have to inherit from PretrainedConfig,
- the __init__ of your PretrainedConfig must accept any kwargs,
- those kwargs need to be passed to the superclass __init__.