[libshumate] scale: Fix background color on dark themes

[Marcus Lundblad <mlundblad src gnome org>]

commit d21ccfe6e604d4a36507e2c46e484a315e52209e
Author: James Westman <james jwestman net>
Date:   Fri Jun 4 12:49:31 2021 -0500

    scale: Fix background color on dark themes
    
    Use the theme background color instead of always setting the background
    to white.

 data/scale.css | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/data/scale.css b/data/scale.css
index 2a22832..249e03e 100644
--- a/data/scale.css
+++ b/data/scale.css
@@ -1,7 +1,7 @@
 map-scale label {
   border: 2px solid rgba(0, 0, 0, 0.5);
   border-top: none;
-  background: rgba(255, 255, 255, 0.5);
+  background: alpha(@theme_bg_color, 0.5);
   padding: 3px;
 }