[gnome-shell-sass] theme: Add message close button styling

[Florian Müllner <fmuellner src gnome org>]

commit a4257f6801d9f97403fdc829709a085d261eac3a
Author: Joonas Henriksson <joonas henriksson gmail com>
Date:   Tue Nov 19 19:40:09 2019 +0200

    theme: Add message close button styling
    
    Since the notification message close button had no border, or mouse
    over effect, there was no way to determine whether the mouse cursor
    were over the button.
    
    Improve this by adding a message-close-button class for the close
    button, and a styling for its hovered state, based on media control
    button styling.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/855

 _common.scss | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/_common.scss b/_common.scss
index bddcedf..cd6eea7 100644
--- a/_common.scss
+++ b/_common.scss
@@ -1152,6 +1152,11 @@ StScrollBar {
             padding: 10px;
           }
 
+          .message-close-button {
+            color: lighten($fg_color, 15%);
+            &:hover { color: darken($fg_color, 10%); }
+          }
+
           .message-media-control {
             padding: 12px;
             color: lighten($fg_color, 15%);