Use CSS to target the image src inside button and replace with another in the Woocommerce Wishlist Plugin for Wordpress

I am using the Woocommerce Wishlist plugin in Wordpress and I want to change the look of the 'Add to Wishlist' button. When I view the source I can see that the button is being styled with a GIF, and I would like to insert my own image into the to give it my own look. Is this possible? Im not sure how to access and edit html inside a plugin. Or can you change the image src somehow via CSS?

this is my website, and the page I am referring to:

http://ift.tt/1woVOYE

Thanks