[libadwaita/wip/exalm/window-border: 1/2] stylesheet: Add a window outline

[Alexander Mikhaylenko <alexm src gnome org>]

commit 14d6e9d65497904e8f5977f57503732845ec4e46
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon Apr 19 21:23:33 2021 +0500

    stylesheet: Add a window outline
    
    Use higher opacity for HighContrast.
    
    Fixes https://gitlab.gnome.org/GNOME/libadwaita/-/issues/131

 src/stylesheet/widgets/_window.scss | 10 ++++++++++
 1 file changed, 10 insertions(+)
---
diff --git a/src/stylesheet/widgets/_window.scss b/src/stylesheet/widgets/_window.scss
index 5cf89d2..5254e20 100644
--- a/src/stylesheet/widgets/_window.scss
+++ b/src/stylesheet/widgets/_window.scss
@@ -12,6 +12,13 @@ window {
                 0 0 0 1px $_wm_border; //doing borders with box-shadow
     margin: 0px;
     border-radius: $window_radius;
+
+    @if $variant == 'dark' {
+      $_window_outline: if($contrast=='high', transparentize(white, .7), transparentize(white, .9));
+      outline: 1px solid $_window_outline;
+      outline-offset: -1px;
+    }
+
     &:backdrop {
       // the transparent shadow here is to enforce that the shadow extents don't
       // change when we go to backdrop, to prevent jumping windows.
@@ -33,6 +40,7 @@ window {
       padding: 0;
       border: solid 1px $borders_color;
       border-radius: 0;
+      outline: none;
       box-shadow: inset 0 0 0 3px $headerbar_bg_color, inset 0 1px $top_hilight;
 
       &:backdrop { box-shadow: inset 0 0 0 3px $backdrop_bg_color, inset 0 1px $top_hilight; }
@@ -43,6 +51,7 @@ window {
   &.fullscreen {
     border-radius: 0;
     box-shadow: none;
+    outline: none;
   }
 
   &.tiled,
@@ -53,6 +62,7 @@ window {
     border-radius: 0;
     box-shadow: 0 0 0 1px $_wm_border_backdrop,
                 0 0 0 20px transparent; //transparent control workaround -- #3670
+    outline: none;
   }
 
   &:backdrop {