-Left-click on a card to add a copy
-Right-click on a card to remove a copy
-Choose whether you want to add/remove a normal or golden copy with the buttons at the top
Everything is saved locally in the browser so as long as you use the same browser and don't manually clear the storage then it's going to stay there. I've tested the site on most modern browsers (it doesn't support older versions of IE yet) and common resolutions but if you find any bugs or got any feature requests/comments, let me know!