gio UI. how to make fullscreen

I want to make a full screen window using the Gio UI framework. But the application is in windowed mode all the time.

As I understood it, this code was supposed to result in a full screen application.

func main() {
    go func() {
        w := app.NewWindow(app.Title("fullscr"),
            app.Fullscreen.Option(),
            app.Decorated(false),
        )

        if err := draw(w); err != nil {
            log.Fatal(err)
        }
    }()
    app.Main()
}

Thanks to @kostix and his comment, I found a solution. I placed w.Option(app.Fullscreen.Option()) in draw function