I just installed some vertical blinds. On top, there is some sort of a decorative "skirt". It is made of a horizontal longitudinal piece and a couple of 90 degree clips, and two short pieces.
I know that there are special rounded clips that allow to make the whole "skirt" from one piece. A pro installed something like that for us in another room and claimed that it was his "proprioetary technology".
I would like to know if such round corners can be bought someplace. Here's a picture of it: