[gtk] Adwaita: Add focus outlines back to scale troughs

[Timm Bäder <baedert src gnome org>]

commit 28482e52beece63bab15d098247739a717ba16a2
Author: Timm Bäder <mail baedert org>
Date:   Sat Feb 15 10:45:33 2020 +0100

    Adwaita: Add focus outlines back to scale troughs
    
    Fixes #189

 gtk/theme/Adwaita/_common.scss | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 14c3877547..5c20871555 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -15,7 +15,6 @@ button:focus(visible),
 checkbutton:focus(visible),
 radiobutton:focus(visible),
 switch:focus(visible),
-scale:focus(visible),
 label:focus(visible),
 row:focus(visible),
 flowboxchild:focus(visible) {
@@ -29,6 +28,14 @@ flowboxchild:focus(visible) {
   outline-width: 1px;
 }
 
+// Widgets that draw their focus indicator outset and not inset
+scale:focus(visible) > trough {
+  outline-color: gtkalpha(currentColor, 0.3);
+  outline-style: dashed;
+  outline-offset: 2px;
+  outline-width: 1px;
+}
+
 
 /***************
  * Base States *
@@ -2584,8 +2591,6 @@ scale {
     }
   }
 
-  &:focus { outline: none; }
-
   // click-and-hold the slider to activate
   &.fine-tune {
     &.horizontal {