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"},