Function floating_edge 

pub fn floating_edge(
    scene: &mut Scene,
    transform: Affine,
    rect: Rect,
    radius: f64,
    theme: &Theme,
)

The 1 px light edge a floating surface carries just inside its outline on a dark material (crate::tokens::Elevation::floating_edge); nothing on a light one. Paint it after the surface’s body and border, at the surface’s own radius: the edge’s radius is concentric with it.