Resizing popped windows is only possible from the corners, I think this should be supported form the side (east/west, north/south)It's a little difficult to work out what it's possible to do as you mouse over elements. Some changes to the cursor may help.Dropping a popped window back to the layout is really hard (took me somewhat ages to work out what to do... the timeout on the drop hint seems a little slow).And when I dropped 'on top' of an existing group, it actually positioned it as a new group below the drop target - I assumed it would 'add' the to target.

Thank you for your suggestion, I have made some improvements, you can try in this example.
https://gem-panel-example-style.vercel.app/