PRANDWOOD'S PROFILE

Hi guys i hope you can help me, i am new at js.
After reading all the .js files, i successfully modified scene_file, as i needed to. My problem is, i cannot find and modify the "savefile" boxes background.
I wold like to use an image but i can olny change the color.

using

ImageManager.loadBitmap("img/system/", "Prova");

in

Window_Selectable.prototype.drawBackgroundRect

nothing is happening

help me please, thank you!!