Byte alignment before writing triangles when making quantized-mesh terrain

From GitHub - CesiumGS/quantized-mesh: Specification for streaming massive terrain datasets for 3D visualization. ,there is a description before the triangle index:

Immediately following the vertex data is the index data. Indices specify how the vertices are linked together into triangles. If tile has more than 65536 vertices, the tile uses the IndexData32 structure to encode indices. Otherwise, it uses the IndexData16 structure.

To enforce proper byte alignment, padding is added before the IndexData to ensure 2 byte alignment for IndexData16 and 4 byte alignment for IndexData32.

Here is my question:
If tile has 100 vertices,how is the data arranged after the vertex data?
[VertexData][1x100x2 bytes blank][IndexData16] or convert IndexData16 to IndexData32?

The padding you describe as [1x100x2 bytes blank] would either be 1 byte of padding, or no padding, depending on what byte count the last byte of [VertexData] ends up on. There would be no reason for multiple hundreds of bytes of padding.

In the case of IndexData32 vertices (because there are more than 65536) there could be anywhere from 0 to 3 bytes of padding to align the start of IndexData to a 4-byte boundary.