[gnome-panel] theme: add hover effect for gp-menu-button

[Alberts Muktupāvels <muktupavels src gnome org>]

commit c421875791c61a960b146529709d360448a43b64
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Sep 13 15:06:07 2018 +0300

    theme: add hover effect for gp-menu-button
    
    This should provide very similar effect to original menu
    button object.

 data/theme/common.css | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/data/theme/common.css b/data/theme/common.css
index b1d4441cc..8c48d7c77 100644
--- a/data/theme/common.css
+++ b/data/theme/common.css
@@ -31,6 +31,10 @@ panel-toplevel.right gp-applet > menubar > .gp-image-menu-item > image:dir(rtl)
   margin-top: 5px;
 }
 
+gp-menu-button:hover .icon {
+  -gtk-icon-effect: highlight;
+}
+
 panel-toplevel.horizontal gp-menu-button {
   padding: 0 2px;
 }