When the doors are closed, is the front of the door flush with the room wal
ls, or is the door set back somewhat from the walls. If it is set back, yo
u could frame the opening on the room side. Any kind of molding that would
fill some of the space between the door and the front of the opening would
be fine, whatever looks best to you. If the front of the door is flush, you
have nothing to do. A piece of trim mounted vertically along the top of t
he opening can be used to hide the sliding track for the doors.