Function paint_pill 

pub fn paint_pill(
    scene: &mut Scene,
    transform: Affine,
    pill: Rect,
    theme: &Theme,
)

Paint the floating pill the window’s own controls stand in: the panel ground of the floating material, at the selector’s radius, over the window’s own ground or over the app’s header row. Every window’s controls stand in this one pill, so a bar says the same thing about them wherever the frame puts them.