Display the results pane above the workspaces. The results pane is somewhat
transparent and has a blue gradient background. The dash pane is slightly
transparent and also has a blue gradient background.
The results pane shows up when a More control is clicked. It disappears when
a Less control is clicked, an area outside of the dash area is clicked,
an item starts being dragged, or the overlay mode is exited.
Add shell_global_create_horizontal_gradient() to shell-global.[ch]
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