This is a simple tealight base for attaching a lithophane. I create the lithophane using this website:

https://3dp.rocks/lithophane/

The base is made for the "Outer Curve" lithophane, sized to 100 mm. I find it works best to set the lithophane to have a 3 mm border around the edge. It doesn't matter whether it's in portrait or landscape mode. When you have the STL file from the website, import the tealight base into Blender, and then import the lithophane. It should automatically sit perfectly aligned on top of the base. Then just export a new STL of the completed tealight. Obviously, it's designed for a battery-operated tealight.