Function set_margin 

pub fn set_margin<Message>(
    id: Id,
    top: i32,
    right: i32,
    bottom: i32,
    left: i32,
) -> Task<Message>

Available on crate feature winit and wayland_platform only.

https://wayland.app/protocols/wlr-layer-shell-unstable-v1#zwlr_layer_surface_v1:request:set_margin