gog_style_stpatrics_simple.user.js

// ==UserScript==
// @name         GOG St Patric's Style Shelf (Simple)
// @namespace    http://nielk1.com/
// @version      1.0
// @description  Apply St Patric's 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">St Patric\'s</b>');
    angular.element(document.querySelector('body')).append(
		'<style type="text/css">'+
		'  .list--grid .product-row-wrapper:after {'+
		'    background-image: url(//images-4.gog.com/54bb846421bb7706daeb066a3b6d6106fe3825b76bec0dffd2fe79151bcc7c83.png) !important;'+
		'  }'+
		'</style>');
})();