My wife likes her K810 bluetooth keyboard - but not its angle or the fact that it slides around the table... So a couple of hours with Rhino3D and here's a simple solution to blutack onto the bottom. (If you did not want it removable, you could use double sided tape)

This will surely also fit a range of small portable keyboards and make them more comfortable to use

Instructions

Simple lofts using Rhino3D and some cutouts using a Grasshopper script I keep around that creates planar voronoi volumes in bounded spaces.

There are recesses for 12mm square rubber feet, which are available in any hobby electronics store...

p.s. sorry about the STL file size; I like fine meshes; it could be much simplified and look pretty much the same, but it really makes no difference given the amount of computer power in ouor hands these days...