Modernize scrollbars
We discussed this with @jsparber in the context of improving notifications/quick settings on small displays, but more generally scrolling behaviors in GNOME Shell could use some modernization. In particular:
- Scrollbars don't have GTK's overlay/hover behavior, so they move the layout off-center (particularly visible in the notification list where it causes uneven padding)
- Scrollviews end with large fade-out gradients. These look a bit old style-wise, and are not as flexible as e.g. Libadwaita's ToolbarView which has just a small optional shadow that doesn't interfere with the usable height
A few suggestions for improving this:
- Scrollbars behave like in GTK (invisible when inactive, overlay, expand on hover, not affecting the layout)
- Maybe we don't actually need scrollbars in some places to begin with? e.g. other OSes don't have scrollbars for notifications either
- When there's fixed toolbars above/below a scrollview the divider shadow should be shown dynamically, matching the AdwToolbarView behavior
- This would require some styling changes in places like the calendar popover, because it requires a full-height split and probably a different color on the two sides, rather than the single background color we have now
Initial mockup applying GTK/Libadwaita scrollbars to the Calendar popover.
