[libadwaita/wip/exalm/arrows] stylesheet: Support arrow menu buttons

[Alexander Mikhaylenko <alexm src gnome org>]

commit 92075ded00e3403ae8c2938c7b9e369d120a4d2a
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Tue Jun 29 12:43:28 2021 +0500

    stylesheet: Support arrow menu buttons
    
    See https://gitlab.gnome.org/GNOME/gtk/-/commit/47b5c68df4e23727886e335db88d989366e4dc2b

 src/stylesheet/widgets/_buttons.scss | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/stylesheet/widgets/_buttons.scss b/src/stylesheet/widgets/_buttons.scss
index fd7fe37b..dd21e2c1 100644
--- a/src/stylesheet/widgets/_buttons.scss
+++ b/src/stylesheet/widgets/_buttons.scss
@@ -338,6 +338,10 @@ button.outline {
 }
 
 menubutton {
+  > button > box {
+    border-spacing: 6px;
+  }
+
   &.osd {
     background: none;
     color: inherit;