Grav\Plugin\Admin\Admin::themes PHP Method

    public function themes($local = true)
    {
        $gpm = $this->gpm();
        if (!$gpm) {
            return false;
        }
        return $local ? $gpm->getInstalledThemes() : $gpm->getRepositoryThemes()->filter(function ($package, $slug) use($gpm) {
            return !$gpm->isThemeInstalled($slug);
        });
    }