Function card_radius 

pub fn card_radius(rect: Rect, theme: &Theme) -> f64

The one floating card: a notification banner, a toast, the command palette, a desk widget’s card, the frame around an app’s call or navigation card. It is the floating Panel’s shape (its radius, capped for a card shorter than two corners) on an opaque ground: the panel ground, the derived panel edge and, on a dark material, the inner light edge, lifted by the floating elevation. Nothing behind a card reads through it; translucency belongs to scrims.