Comment by exmadscientist

For anyone wondering how a "professional" would do this, you might use a 3D CAD program like SolidWorks, Inventor, or FreeCAD. You'd make a single 2D sketch, draw some lines in box shapes, and put some constraints on those boxes. Free/unbound dimensions would read out the distances that you needed to know. The whole thing would take less than five minutes for someone with beginner-level skills (i.e., me), and maybe an hour or two to learn from scratch. It's not as cool as doing this with CSS's constraint solver, but it might add a new tool to your toolbox, and the value of that is difficult to overestimate.