[libadwaita/wip/exalm/background-colors: 39/54] stylesheet: Simplify tree headers

[Alexander Mikhaylenko <alexm src gnome org>]

commit 9a140a7712950ede1b3fb703113a24641bd27c83
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Wed Sep 1 13:47:25 2021 +0500

    stylesheet: Simplify tree headers
    
    Remove one more instance of mixing.

 src/stylesheet/widgets/_trees.scss | 41 ++++++++++++--------------------------
 1 file changed, 13 insertions(+), 28 deletions(-)
---
diff --git a/src/stylesheet/widgets/_trees.scss b/src/stylesheet/widgets/_trees.scss
index 1d4b954d..0edfc9fd 100644
--- a/src/stylesheet/widgets/_trees.scss
+++ b/src/stylesheet/widgets/_trees.scss
@@ -71,28 +71,29 @@ treeview.view {
 
   > header {
     > button {
-      $_column_header_color: mix($fg_color, $base_color, 50%);
+      @extend %undecorated_button;
+      padding: 0 6px;
+      border: 1px solid gtkalpha($text_color, .15);
+      border-width: 0 0 1px 1px;
+      border-radius: 0;
 
-      @extend %column_header_button;
+      &:disabled {
+        border-color: $bg_color;
+      }
 
-      color: $_column_header_color;
-      background-color: $base_color;
+      &:last-child { border-right-width: 0; }
+
+      color: gtkalpha($text_color, .4);
       font-weight: bold;
       box-shadow: none;
 
       &:hover {
-        @extend %column_header_button;
-
-        color: mix($_column_header_color, $fg_color, 50%);
+        color: gtkalpha($text_color, .7);
         box-shadow: none;
-        transition: none; //I shouldn't need this
       }
 
       &:active {
-        @extend %column_header_button;
-
-        color: $fg_color;
-        transition: none; //I shouldn't need this
+        color: $text_color;
       }
       sort-indicator {
         &.ascending {
@@ -128,22 +129,6 @@ treeview.view {
   }
 }
 
-%column_header_button {
-  padding: 0 6px;
-  background-image: none;
-  border-style: solid;
-  border-width: 0 0 1px 1px;
-  border-color: $borders_color;
-  border-radius: 0;
-
-  &:disabled {
-    border-color: $bg_color;
-    background-image: none;
-  }
-
-  &:last-child { border-right-width: 0; }
-}
-
 /********************************************************
  * Data Tables                                          *
  * treeview like tables with individual focusable cells *