[gnome-shell] theme/window-picker: Add box-shadow to the workspace background

[Marge Bot <marge-bot src gnome org>]

commit 135c9194cd50b20b8bab5865394a738670a8baee
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Mon Feb 8 16:43:32 2021 +0100

    theme/window-picker: Add box-shadow to the workspace background
    
    According to the GNOME 40 mockups, add a box-shadow to the workspace
    background. For this to work, we also need a background-color (St
    limitations), and to make sure that background-color doesn't bleed over
    the rounded corners of the wallpaper, we also need to tell St to use a
    border-radius and clip the background-color painting using a rounded
    path.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1651>

 data/theme/gnome-shell-sass/widgets/_window-picker.scss | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/data/theme/gnome-shell-sass/widgets/_window-picker.scss 
b/data/theme/gnome-shell-sass/widgets/_window-picker.scss
index 1432a3bf81..7592aa4c9d 100644
--- a/data/theme/gnome-shell-sass/widgets/_window-picker.scss
+++ b/data/theme/gnome-shell-sass/widgets/_window-picker.scss
@@ -44,3 +44,10 @@ $window_close_button_padding: 3px;
     background-color: darken($osd_bg_color, 5%);
   }
 }
+
+.workspace-background {
+  // keep in sync with BACKGROUND_CORNER_RADIUS_PIXELS in workspace.js
+  border-radius: 30px;
+  background-color: $osd_bg_color;
+  box-shadow: 0 -4px 16px 4px transparentize(darken($osd_bg_color, 30%), 0.7);
+}