use gpui::*; struct Shadow {} impl Render for Shadow {    fn render(&mut self, _cx: &mut ViewContext<Self>) -> impl IntoElement {        div()            .flex()            .bg(rgb(0xffffff))            .size_full()            .justify_center()            .items_center()            .child(div().size_8().shadow_sm())    }} fn main() {    App::new().run(|cx: &mut AppContext| {        let bounds = Bounds::centered(None, size(px(300.0), px(300.0)), cx);        cx.open_window(            WindowOptions {                window_bounds: Some(WindowBounds::Windowed(bounds)),                ..Default::default()            },            |cx| cx.new_view(|_cx| Shadow {}),        )        .unwrap();    });}