With the CSS Grid visual helpers turned on it’s possible to see how html elements are placed on the grid, but the helpers will only show you the definition of the explicit grid (as you have defined it).
When element placement relies on auto-rows or auto-columns to add rows/columns as needed, those grid boundaries are not shown in PG. And neither are grid lines or areas.
It would help a great deal for PG to show more info about the grid def and placement of elements, similar to how they are shown using the developer tools in firefox.