I tend to design rooms with cornice boards but many of my clients have question when I use the term, "Cornice Board". This is a window treatment that is very simple, something to add framing, texture and color to the window. It is simply a board covered in a padding material and then that is covered in your choice of decorative material. It can either be straight or shaped, see the samples below.
(Above) - This is a shaped cornice box. Underneath this treatment there could be a blind that is more functional. I do like how the window and sink treatment coordinate.
(Above) - This is a straight cornice box, very appropriate for this space. Had the client also desired, you could have hung long panels underneath this cornice which would further frame the window. The geometric cornice fabric all lends to the transitional feeling of the room. Off subject, but worth a notice, do you see all of the different pillow fabrics . . . loving it!