[gnome-builder] themes: Explicitly specify i-wanna-be-listbox regular background color

[Christian Hergert <chergert src gnome org>]

commit fcc4f9344486c32593ceee7a8f8753ea17c5655b
Author: vanadiae <vanadiae35 gmail com>
Date:   Wed Jun 30 16:29:27 2021 +0200

    themes: Explicitly specify i-wanna-be-listbox regular background color
    
    While having a transparent background works fine for the most simple
    tree views, when there's drag and drop involved it breaks because the
    dragged row has a black background, so the text is unreadable and it
    is expected that the row keeps its "real" background color there.
    
    So to fix this, this commit sets the background color to the
    theme_base_color.

 src/libide/themes/themes/shared/shared-treeview.css | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/libide/themes/themes/shared/shared-treeview.css 
b/src/libide/themes/themes/shared/shared-treeview.css
index 9f595fb90..901c29c53 100644
--- a/src/libide/themes/themes/shared/shared-treeview.css
+++ b/src/libide/themes/themes/shared/shared-treeview.css
@@ -1,6 +1,6 @@
 treeview.i-wanna-be-listbox {
   color: @theme_fg_color;
-  background: transparent;
+  background-color: @theme_base_color;
 }
 treeview.i-wanna-be-listbox:hover {
   background-color: alpha(@theme_fg_color, 0.05);