код для добавления собственных иконок в custom.js

custom-uikit-icons.js

/* my custom icons */

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define('uikiticons', factory) :
    (global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.UIkitIcons = factory());
})(this, (function () { 'use strict';

    function plugin(UIkit) {
      if (plugin.installed) {
        return;
      }

      UIkit.icon.add({
        "youtube": "<svg width=\"20\" height=\"20\" viewBox=\"0 0 20 20\" xmlns=\"http://www.w3.org/2000/svg\"><path d=\"M15,4.1c1,0.1,2.3,0,3,0.8c0.8,0.8,0.9,2.1,0.9,3.1C19,9.2,19,10.9,19,12c-0.1,1.1,0,2.4-0.5,3.4c-0.5,1.1-1.4,1.5-2.5,1.6 c-1.2,0.1-8.6,0.1-11,0c-1.1-0.1-2.4-0.1-3.2-1c-0.7-0.8-0.7-2-0.8-3C1,11.8,1,10.1,1,8.9c0-1.1,0-2.4,0.5-3.4C2,4.5,3,4.3,4.1,4.2 C5.3,4.1,12.6,4,15,4.1z M8,7.5v6l5.5-3L8,7.5z\"/></svg>"
      });
    }

    if (typeof window !== 'undefined' && window.UIkit) {
      window.UIkit.use(plugin);
    }

    return plugin;

}));