1. You can add a label text to the quantity input in the file woocommerce / global / quantity-input.php.

Hi, is there anyway that I can do something like this.
If the category of product is A, then the display price should be $ 12/mm
If the category of product is B, then the display price should be $ 30

Secondly, how can I change the font ONLY for the price on product details page, eg. Arial to Tahoma ?

Regards