[gnome-shell-sass] common: Restore drag effect between workspaces

[Alessandro Bono <abono src gnome org>]

commit de41fb43a58e3b10b9f7df83904bd9e0e381637b
Author: Alessandro Bono <abono gnome org>
Date:   Tue Oct 17 16:34:14 2017 +0200

    common: Restore drag effect between workspaces
    
    When dragging a window between two workspaces a light effect used
    to be present. The effect was lost probably during the theme revamp
    in version 3.16.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789103

 _common.scss |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/_common.scss b/_common.scss
index 306de6a..ea36774 100644
--- a/_common.scss
+++ b/_common.scss
@@ -1462,6 +1462,12 @@ StScrollBar {
     border-radius: 9px 0 0 9px;
     //border-width: 1px 0 1px 1px; //fixme: can't have non unoform borders :(
     &:rtl { border-radius: 0 9px 9px 0;}
+
+    .placeholder {
+      background-image: url("resource:///org/gnome/shell/theme/dash-placeholder.svg");
+      background-size: contain;
+      height: 24px;
+    }
   }
   .workspace-thumbnail-indicator {
     border: 4px solid $selected_bg_color;