Add scroll shadows to indicate more items available

[rouilj]

On android the scroll bar is narrow and difficult to see.

Add scroll shadows to the command list to indicate that there are more items available.

Note the white shadows/light showing at the top and bottom since the list can scroll to either side. If we were at the bottom, only the top shadow/light would be shown.

CSS generated with: https://css-scroll-shadows.vercel.app

Ref: https://lea.verou.me/2012/04/background-attachment-local/ https://css-tricks.com/books/greatest-css-tricks/scroll-shadows/