Using Safari on iOS 15: Scroll this page down a bit so that the Safari address bar collapses. Then press the "Click to make..." button. Notice how after the button is pressed that the bottom bar, which is supposed to be fixed to the bottom of the screen, has space between it and the bottom of the window. Its position seems to be based off the assumption that the address bar is no longer collapsed -- which if the page intiailly wasn't scrollable, would be true because if the page doesn't have a scrollable body then the address bar would never collapse. If you view this demo on iOS14, this problem doesn't happen.