Created attachment 354323 [details]
Test case to reproduce the flexibe box issue
Check the attached examples, the issue is more noticeable in Grid Layout but it also happens on Flexbox.
The problem is that the items have a child with 100% width and height.
The items also have margin, padding, border and scrollbar.
The scrollbar size is ignored so the items end up being bigger than expected,
causing overflow (so you can actually scroll) when it was supposed to not happen.
Created attachment 354324 [details]
Test case to reproduce the grid box issue