Stackable box without support

This is a remix of https://www.thingiverse.com/thing:647425.

I printed the thing and found a few things that could be improved.

1. Less material, shorter printing time
I could spare much material and time by reducing the wall thickness and placing ribs instead, not compromising the strength and the stiffness.
That made my model weighing about 45g, with about 3-4 hours of printing time with the layer height of 0.25 mm.

2. Wider ledge
I also found that the ledge of the previous model w