Add overscroll-behavior css which is supported in modern browsers
Enable guess area scrolling even if the focus is in the keyboard UI, by making the keyboard UI a sticky element
From this change, the scroll bar became visible on the guess UI and the keyboard UI.
However, in Safari browser, the scrollbar is placed behind the sticky UI.
This problem is handled by adding small margin-x in the sticky keyboard UI, assuming the scrollbar width is smaller than the margin in various environments (checked in Safari, iOS 15.7)
overscroll-behaviorcss which is supported in modern browsersClose #6