[gnome-shell] theme: Remove background-color from .workspace-background

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

commit 374a2b2c511d2781492a96520f24a93e6da196f6
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Thu May 27 17:47:14 2021 +0800

    theme: Remove background-color from .workspace-background
    
    It's not visible because it's covered by the actual wallpaper, so
    not rendering it eliminates most of the render time for
    `workspace-background`, without changing its appearance.
    
    When animating the overview by tapping Super, this reduces the
    shell's overall render time by about 15%.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1904>

 data/theme/gnome-shell-sass/widgets/_window-picker.scss | 1 -
 1 file changed, 1 deletion(-)
---
diff --git a/data/theme/gnome-shell-sass/widgets/_window-picker.scss 
b/data/theme/gnome-shell-sass/widgets/_window-picker.scss
index b3b93f291a..fa3f191945 100644
--- a/data/theme/gnome-shell-sass/widgets/_window-picker.scss
+++ b/data/theme/gnome-shell-sass/widgets/_window-picker.scss
@@ -48,6 +48,5 @@ $window_close_button_padding: 3px;
 .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);
 }