Function extract_shadows 

pub fn extract_shadows(main: &mut World, render: &mut World)

Extract fn that emits one ExtractedShadow per entry in Visuals::shadows. A drop shadow is placed at rect.order - 1 + idx so it paints under the source rect and stacked shadows keep source order. An inset shadow takes the rect’s own order: it paints over the background and under the border, as CSS draws it.