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

[Florian Müllner <fmuellner src gnome org>]

commit fde7e3b4c0416e60d6760a2c6c00dde6950d8f7c
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>

 widgets/_screen-shield.scss | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/widgets/_screen-shield.scss b/widgets/_screen-shield.scss
index 00c549a..e289fdb 100644
--- a/widgets/_screen-shield.scss
+++ b/widgets/_screen-shield.scss
@@ -66,7 +66,7 @@
 }
 
 #lockDialogGroup {
-  background-color: lighten(#2e3436, 8%);
+  background-color: $system_bg_color;
 }
 
 #unlockDialogNotifications {