gtk:render-background (context cr x y width height)

context -- a gtk:style-context object
cr -- a cairo:context-t context
x -- a number coerced to a double float with the x origin of the render area
y -- a number coerced to a double float with the y origin of the render area
width -- a number coerced to a double float with the rectangle width
height -- a number coerced to a double float with the rectangle height

Renders the background of an element.