A "cornice box" refers to a decorative structure that is installed above windows to make them look more elegant. It is like a wooden frame placed on top of the window that adds a stylish touch to the overall appearance of a room. Full definition
Seeing the pic with the black cornices makes me wonder, are cornice boxes still «in?» (theinspiredroom.net)
We also offer decorative cornice boxes to take your interior design to the next level. (budgetblinds.com)
A built - in window seat with storage stands under a picture window dressed in a white curved cornice box finished with silver nailhead trim flanked by built - in bookcases. (homebunch.com)