How can I add horizontal lines between products on my packing slip?

[SarahBrymer]

Hello,

I am trying to make the packing slip more user friendly. I can't figure out how to have Shopify automatically add horizontal lines between each product ordered. Any suggestions?Below is a screenshot as an example (color green is just for attention, I would like them to be black) My site is grandcircuitproducts.com. Thank you!