overshoot=1;

face_plate(
  box_width  = 200,
  box_height =  90,
  box_depth  =  25
);

module face_plate( box_width, box_height, box_depth, wall_thickness=5) {
  difference() {
    cube([
      box_width,
      box_depth,
      box_height
    ]);
    translate([
      wall_thickness/2,
      0-overshoot,
      wall_thickness/2
    ])
      cube([
        box_width-wall_thickness,
        box_depth-wall_thickness+overshoot,
        box_height-wall_thickness
      ]);
  }
}