A box with rounded corners and lid. Many parameters can be adjusted in the .scad file included.

Small box pictured is printed with the value in the included .scad file, except that $fa=10. Both boxes printed with 2 shells, layer height 0.27 mm and 5% infill.

Both the box and lid can be a bit hard to remove from baseplate as they have a huge contact area. This especially goes for large boxes.

Note that roundness must be higher than thickness.