Piwik\Plugin\Manager::getTheme PHP Method

    public function getTheme($themeName)
    {
        $plugins = $this->getLoadedPlugins();
        foreach ($plugins as $plugin) {
            if ($plugin->isTheme() && $plugin->getPluginName() == $themeName) {
                return new Theme($plugin);
            }
        }
        throw new \Exception('Theme not found : ' . $themeName);
    }