How to generate gradient hexahedral mesh using Neper

[cqZ2021]

I want to construct grain boundary elements, which require a finer mesh. However, the grain size used is 60 μm. If the mesh size used for the entire model is the same as the grain boundary, the calculation time will be very long. Therefore, I want to generate a gradient hexahedral mesh by generating a fine mesh at the grain boundary and a coarse mesh inside the grain. Please tell me how I should do this?