$fn=120;
//include <./BOSL2/std.scad>
//include <./BOSL2/rounding.scad>

A=30.8;
I=26.8;
R=2;

intersection() {
  minkowski() {
    cube([A-2*R,A-2*R,6], center=true);
    sphere(r=R);
  }
  translate([-30,-30,0]) mirror([0,0,1]) cube(60);
}
translate([0,0,10]) 
difference() {
  #cube([I,I,20], center=true);
  cube([I-3,I-3,21], center=true);
}