gtk:snapshot-append-outset-shadow (snapshot outline color dx dy spread radius)

snapshot -- a gtk:snapshot object
outline -- a gsk:rounded-rect instance for the outline of the region surrounded by the shadow
color -- a gdk:rgba instance for the color of the shadow
dx -- a number coerced to a single float for the horizontal offset of shadow
dy -- a number coerced to a single float for the vertical offset of shadow
spread -- a number coerced to a single float representing how far the shadow spreads towards the outside
radius -- a number coerced to a single float representing how much blur to apply to the shadow

Appends an outset shadow node around the box given by outline.