scroll up and down buttons with settings

Adds up/down buttons, transparency toggle, and a settings panel with a hide timer.

this is a very helpful userscript that allows you to scroll to the top and bottom of a web page.

Marjanoo edition - where you have the option to make the button transparent (so that the buttons won't get in the way):
https://greasyforks.org/en/scripts/546045-scroll-up-and-down-buttons?version=1664766