Two distinct failure cases here, one worse than the other:
One, at window widths slightly above 800px, the panels are on the right jut off the right-hand edge of the window and cause horizontal scrolling, which is bad.
Two, at window widths below 800px, the panels move down to the bottom (good) but they hug the right-hand side of the window and leave a lot of unused blank space on the left (not so good). This isn't terrible in the same way that horizontal scrolling is, but it could be better.
Two distinct failure cases here, one worse than the other:
One, at window widths slightly above 800px, the panels are on the right jut off the right-hand edge of the window and cause horizontal scrolling, which is bad.
Two, at window widths below 800px, the panels move down to the bottom (good) but they hug the right-hand side of the window and leave a lot of unused blank space on the left (not so good). This isn't terrible in the same way that horizontal scrolling is, but it could be better.