gtk:snapshot-append-border (snapshot outline widths colors)

snapshot -- a gtk:snapshot object
outline -- a gsk:rounded-rect instance for the outline of the border
widths -- a list of 4 numbers coerced to single floats for the stroke width of the border on the top, right, bottom, and left side respectivly
colors -- a list of 4 gdk:rgba instances for the colors used on the top, right, bottom, and left side

Appends a stroked border rectangle inside the given outline. The four sides of the border can have different widths and colors.