gog_style_pinata_simple.user.js

// ==UserScript==
// @name         GOG Piñata Style Shelf (Simple)
// @namespace    http://nielk1.com/
// @version      1.0
// @description  Apply Piñata style to your account shelf
// @author       You
// @match        https://www.gog.com/*/account
// @match        https://www.gog.com/*/account/movies
// @match        https://www.gog.com/*/account/wishlist
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var styleSelector = angular.element(angular.element(document.getElementsByClassName('skin-selector')).children()[0]);
    styleSelector.children().remove();
    styleSelector.append('<b class="skin-selector__current">Piñata</b>');
    angular.element(document.querySelector('body')).append(
		'<style type="text/css">'+
		'  .list--grid .product-row-wrapper:after {'+
		'    background-image: url(//images.gog.com/20c8c72937e3f6d194f21314d6e575582bdfceeee5f592fc974be29491791d81.png) !important;'+
		'  }'+
		'</style>');
})();