[gnome-shell] theme/screen-shield: Use the same background color as in the overview

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

commit bd7e3f4d6b16435912ab10a857d80b9f7525bef3
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Thu Mar 4 08:40:23 2021 +0100

    theme/screen-shield: Use the same background color as in the overview
    
    The overview uses $system_bg_color as its background color, and since we
    nowadays show the overview right after starting up, it makes sense to
    use the same background color for the login screen.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3812
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1742>

 data/theme/gnome-shell-sass/widgets/_screen-shield.scss | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/data/theme/gnome-shell-sass/widgets/_screen-shield.scss 
b/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
index 00c549a535..e289fdbaf6 100644
--- a/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
+++ b/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
@@ -66,7 +66,7 @@
 }
 
 #lockDialogGroup {
-  background-color: lighten(#2e3436, 8%);
+  background-color: $system_bg_color;
 }
 
 #unlockDialogNotifications {