StyledWidget and StyledComposite (in ej.library.ui#widget 2.x) have the following class hierarchy.
An object implementing the interface Renderable is an object that is intended to be rendered on the screen.
A Widget is the superclass of all the user interface objects.
A StyledRenderable represents a renderable with a style.
StyledWidget and StyledComposite are Widget and Composite that implement Element. Therefore, they contain a style (retrieved from the stylesheet), and apply boxing (margin, border, background, padding) before rendering their content.