Module layers 

Layers

Layers control the rendering order of elements. Elements in higher layers are rendered on top of those in lower layers.

Use the .layer() method with one of three variants:

• Layer::Relative(i16) (default): relative layer to the parent’s layer. 0 keeps the normal stacking order, negative values move behind siblings and positive values in front.
• Layer::Overlay: adds a big layer jump relative to the parent’s layer. You may stack multiple overlays on top of each other.
• Layer::OverlayLevel(u8): paint on a specific, numbered overlay level, regardless of the parent’s layer. There are up to 16 levels you can use, anything above will be capped at 16.

fn app() -> impl IntoElement {
    rect()
        .child(rect().layer(-1).child("Background")) // below default
        .child(rect().child("Content")) // default layer
        .child(rect().layer(1).child("Foreground")) // above default
        .child(rect().layer(Layer::Overlay).child("Modal")) // on top of everything
}

Note: The rendering order of elements within the same layer is not guaranteed. Always use distinct layer values when order matters.