[libadwaita/wip/exalm/borders] stylesheet: Make sure header bar borders have contrast

[Alexander Mikhaylenko <alexm src gnome org>]

commit 2a1b259b474b8cdbd88eab81f184df0b60d1f0f8
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Wed Jul 21 16:41:08 2021 +0500

    stylesheet: Make sure header bar borders have contrast
    
    Use the same trick with negative margins as we've been using with solid-csd.
    It's not particularly good but since nobody had complained about it for
    years, should be good enough.
    
    This should also fix the long-standing issue of discolored separators between
    recolored header bars.

 src/stylesheet/widgets/_header-bar.scss | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
---
diff --git a/src/stylesheet/widgets/_header-bar.scss b/src/stylesheet/widgets/_header-bar.scss
index 9d04ee94..e8b844a3 100644
--- a/src/stylesheet/widgets/_header-bar.scss
+++ b/src/stylesheet/widgets/_header-bar.scss
@@ -1,10 +1,15 @@
 headerbar {
   min-height: 46px;
-  box-shadow: inset 0 -1px $borders_color;
+  box-shadow: inset 0 -1px transparentize($text_color, .9),
+              inset  1px 0 transparentize($text_color, .9),
+              inset -1px 0 transparentize($text_color, .9);
   background-color: $headerbar_bg_color;
 
+  margin-left: -1px;
+  margin-right: -1px;
+
   > windowhandle > box {
-    padding: 0 6px;
+    padding: 0 7px;
 
     &,
     > box.start,
@@ -54,8 +59,6 @@ headerbar {
   .solid-csd & {
     &:backdrop, & {
       &:dir(rtl), &:dir(ltr) { // specificity bump
-        margin-left: -1px;
-        margin-right: -1px;
         margin-top: -1px;
       }
     }