[gnome-shell-extensions] classic: fix a broken build

[Jakub Steiner <jimmac src gnome org>]

commit b138e218bb5f215293d0b08bca1387fe92cc109f
Author: Jakub Steiner <jimmac gmail com>
Date:   Mon Jun 24 20:28:03 2019 +0200

    classic: fix a broken build
    
    - redesign of the default theme nuked some local variables
      breaking the build.

 data/gnome-classic.scss | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/data/gnome-classic.scss b/data/gnome-classic.scss
index 9e23506..410c5f0 100644
--- a/data/gnome-classic.scss
+++ b/data/gnome-classic.scss
@@ -60,9 +60,9 @@ $variant: 'light';
   &.lock-screen,
   &.unlock-screen, 
   &.login-screen { 
-    background-color: transparentize($_bubble_bg_color, 0.5);
-    background-gradient-start: transparentize($_bubble_bg_color, 0.5);
-    background-gradient-end: transparentize($_bubble_bg_color, 0.5);
+    background-color: transparentize($bg_color, 0.5);
+    background-gradient-start: transparentize($bg_color, 0.5);
+    background-gradient-end: transparentize($bg_color, 0.5);
     border-bottom: none;
     .panel-button { color: $osd_fg_color; }
   }