[Plugin: Easy FancyBox] Custom Close button "X"

Hey, I like the plugin so far it’s doing exactly what I need. I just have 1 question so far. I want to replace the existing close “X” with my own close button. I assume if I edit the actual plugin CSS it will get replaced if the plugin updates. I know some other plugins allow you to copy the CSS to your themes folder and then edit it there to avoid any issues. Does fancy-box allow that? Otherwise how would I do that? what code do I need to put on a image to allow it to close the overlay?

Thanks

https://www.ads-software.com/extend/plugins/easy-fancybox/