@user:57123 you can do that :

Manipulate[
 Show[a = {
FaceForm[Red,col], Cuboid[{2, 2, 2}, {5, 5, 5}],
FaceForm[col,Red],Cuboid[{2, 2, 2} + thickness,  {5, 5, 5} - thickness],
Green, Ellipsoid[{8, 8, 8}, {2, 2, 2}]};
{
   Graphics3D[{a}, PlotRange -> {{0, 10}, {0, 10}, {0, 10}},
    Boxed -> True, ImageSize -> {300, 300},
    ClipPlanes -> {i, j, 1, -k + 0.01},
    ClipPlanesStyle -> {Directive[Opacity[.3], Blue]}]}],
 "Plane",
 {{i, 0, "X"}, 0, 2, .01, ImageSize -> Small, Appearance -> "Labeled"},
 {{j, 0, "Y"}, 0, 2, .01, ImageSize -> Small, Appearance -> "Labeled"},

@JasonB. Excellent, thanks!

@P.Fonseca Nassim Taleb on Paul Romer's essay twitter.com/nntaleb/status/986607864180441088

@Zviovich and I just noticed that WR add a reply on the PDF subject... Interesting debate. Doesn't take us anywhere, but still interesting...