code: function getInheritTheme(theme, tree = {}) {
    if (!app.locals.themes[theme]) {
      // this theme is not installed
      app.error('requested theme:%s but it is not installed', theme);
      return tree;
    }
  
    // add the one been requested
    tree[theme] = {};
  
    // get inheritance
    var config = app.locals.themes[theme].zealderConfig;
    if (config && config.themeDependency && !tree[config.themeDependency]) {
      tree = getInheritTheme(config.themeDependency, tree);
    }
  
    return tree;
  }
docs: get theme inheritance