two improvement could been made for better browsing experience

1. one button click for only one page up or down instead of top or bottom, so that long page easier to read. it need an other arrow icon, movable along the screen edge by dragging to mark a distance from the bottom of the screen to show how much of a full screen to be scrolled up or down for one click. so that it just scrolls only one page of scrollabe content for each button click. the mark is needed for pages with fixed header or footer permanently occuping top or bottom part of the screen that is resistant to be scrolled.

2. continuous button pressing scrolls page quickly till top or bottom reached.