Hi @Xapod,
Trancparancy is not supported in 2D views, you can use a viewfilter to make the Railing transparent, the (top)rail/posts will also become transparent but depending the scale it won't be noticable.
If you don't want the posts/rails to become transparant, then define the mesh in the toprail (in reality the mesh will also run along the posts), and because the toprail is a seperate subcategory and shared, it can be overwritten by a viewfilter without making the posts/rails transparent. Note: in the viewfilter use the category Railing > TopRail for this to work with the toprail.
Below a sample with the mesh defined in the TopRail + viewfilter in the topleft view.

Another option would be to use a 3D view as Elevation.
- Michel