This is my first time using a material in Unreal Engine. I am trying to create a transparent cube except for the inner face of the base, which I would like to be opaque white, like in this drawing:

[![cube with transparent sides and an opaque white inner base][1]][1]

I have created a cube with transparent sides and an opaque white top:

[![blueprint of a cube with transparent sides and an opaque white top][2]][2]

I am attempting to paint the top face with a semi-transparent blue, like the sides, and move the upward-facing painting of that face down to the base, but that is not going well:

[![blueprint produing a cube with transparent sides and an opaque blue top][3]][3]

How might I achieve this material? I am using the material on glTF cubes in 3dtiles. They accept materials in the same way as a static mesh does, but it is not possible to identify the vertices.


  [1]: https://i.sstatic.net/p0JtV.png
  [2]: https://i.sstatic.net/RWS5z.png
  [3]: https://i.sstatic.net/D9V4A.png