Woocommerce refund

Hi,

I have a question about the refund option in Woocommerce.

I have an order, which is set to pending (Not yet approved) and I want to refund, for instance 20$ of the total amount of 40$. Does that mean the full amount of 40$ is withdrawn and then afterwards the customer will get the 20$ refund?

Or does it mean, that the customer only will be charged 20$ (40$ – 20$) ?