Hi,

Want to look into this, can you assign?

I'm fine if you want to take a look, there seem to be issues in Chromium and Firefox.
I cannot assign it to you, so I'm adding myself as owner,
but I won't be working on this, I'd just be following your progress here.

Check this example:
https://jsbin.com/fawabav/1/edit?html,css,output

I believe behavior in 2.A) is wrong in Chromium.
And behavior in 1.B) is wrong in Firefox.

The problem is that a "1fr" row is equivalent to "minmax(auto, 1fr)",
and the item has by default "min-height: auto",
so that forces the row to be as tall as the item's height.

Then when you have scrollbar "min-height: auto" doesn't apply,
so the row should only use the avialable space.

Mmmm, probably I spoke too fast.
When we have "height: 100%" on the item, I don't think the "min-height: auto" should have any effect. So 1.A) is probably bad in Chromium and Firefox.
2.A) seems wrong in Chromium too.

All this stuff is quite complex, so we need to debug properly the track sizing algorithm
to understand the issue.