The Black Ice stairs model is just a black recolor of the sandstone stairs - expected / hoped for a cleaner, sharper look in line with the difference between the wobbly sandstone foundations and the black ice foundations.
The black ice wedge foundation does not line up next to black ice wall pieces - there’s a wide gap between them. I think that attaching fence foundation as cladding to the outside of the wedge fixes it but the snapping model has chosen this particular part of my building to refuse to work. (of course there are lots of strange and invalid looking placements that do work, but not the one that seems obvious. Grr.)