[gtk] Adwaita: Fix selection in vertical spin buttons

[Matthias Clasen <matthiasc src gnome org>]

commit 1f7469575890aee786dc87f60cec585193f29b46
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Feb 7 15:42:32 2020 -0500

    Adwaita: Fix selection in vertical spin buttons
    
    This was broken by more specific selectors.

 gtk/theme/Adwaita/_common.scss | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 4028bb0988..a1f1a66545 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1203,6 +1203,8 @@ spinbutton {
       min-width: 32px;
       padding: 0;
       border-radius: 0;
+
+      > selection { @extend %selected_items; }
     }
 
     > button {