[gtk/wip/jimmac/flat-button-tweaks] Adwaita: flat button adjustments

[Jakub Steiner <jimmac src gnome org>]

commit 0001e7298224cb68148cdb34f5568fee7c533474
Author: Jakub Steiner <jimmac gmail com>
Date:   Thu Dec 17 11:19:46 2020 +0100

    Adwaita: flat button adjustments
    
    - normally lighter (on bg_color)
    - darker for headerbar
    - undecorated checked buttons were never style properly (even gtk3)
      see page2 volume buttons
    
    Finetunes https://gitlab.gnome.org/GNOME/gtk/-/issues/3427

 gtk/theme/Adwaita/_common.scss  |  7 +++++--
 gtk/theme/Adwaita/_drawing.scss | 16 ++++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 90b09a635f..88bffad42e 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -540,6 +540,9 @@ button {
         @include button(undecorated-active);
         transition: $button_transition;
       }
+      &:checked {
+        @include button(undecorated-checked);
+      }
       &:backdrop, &:disabled, &:backdrop:disabled { @include button(undecorated); }
     }
 
@@ -1396,9 +1399,9 @@ windowcontrols {
     min-height: 0;
     &:hover {
       //special case hover colors inside a headerbar
-      @include button(undecorated-hover,$c:$headerbar_bg_color);
+      @include button(undecorated-hover,$c:darken($headerbar_bg_color,10%));
     }
-    &:active { @include button(undecorated-active,$c:$headerbar_bg_color); }
+    &:active { @include button(undecorated-active,$c:darken($headerbar_bg_color,10%)); }
   }
 }
 
diff --git a/gtk/theme/Adwaita/_drawing.scss b/gtk/theme/Adwaita/_drawing.scss
index dd45692767..1d30123b25 100644
--- a/gtk/theme/Adwaita/_drawing.scss
+++ b/gtk/theme/Adwaita/_drawing.scss
@@ -419,7 +419,7 @@
     box-shadow: none;
     text-shadow: none;
     @if $variant == 'light' {
-      background-color: darken($c,26%);
+      background-color: darken($c,14%);
     }
     @else {
       background-color: darken($c,10%);
@@ -431,12 +431,24 @@
     box-shadow: none;
     text-shadow: none;
     @if $variant == 'light' {
-      background-color: darken($c,40%);
+      background-color: darken($c,30%);
     }
     @else {
       background-color: darken($c,14%);
     }
   }
+  @else if $t==undecorated-checked {
+    border-color: transparent;
+    background-image: none;
+    box-shadow: none;
+    text-shadow: none;
+    @if $variant == 'light' {
+      background-color: darken($c,20%);
+    }
+    @else {
+      background-color: darken($c,12%);
+    }
+  }
 }
 
 @mixin headerbar_fill($c:$headerbar_bg_color, $hc:$top_hilight, $ov: none) {