Gray box around paypal image

I have been looking through posts on removing the gray border that surrounds an image. It seems as though usually when there is one, there is some sort of alignment problem, or one needs to change something in the CSS. I am very new to this and have little knowledge but am trying to learn how to troubleshoot these issues. I don’t know what a css is really besides that it helps to give a more inside look into the website? I want to somehow remove the gray border around my paypal link that i have inserted in my csa page. Is there a simple way to do it? I have a chunk theme.

https://roserootherbes.wordpress.com/csa/

Thanks