Better custom GroupRow example?

[PierrickLozach]

I have looked at https://codesandbox.io/s/customizing-grouprow-material-table-forked-tcegil?file=/src/index.js to understand how a custom GroupRow can be created.

However, when opening a row, it looks different than what the row should really look like. Note how the birth year and city are not aligned with the headers.

How can I use a custom row and keep the same formatting as the original row when using a custom GroupRow?

Thanks