GTK3 & GTK4 tweaks

- Recover thunar's root-warning banner
- Reduce size of thunar's root-warning banner
- Move panel-background color to _colors.scss
- Lighten gtk4 button's color to match gtk3
- Use lighter color for tabs

src/themes/Kali/sass/gtk4/_common-tweaks.scss

@@ -284,7 +284,6 @@ notebook {
 
           &:checked {
             @include button(normal);
-            background: $base_color;
 
             &:backdrop {
               @include button(backdrop);

src/themes/Kali/sass/gtk4/upstream/_drawing.scss

@@ -133,7 +133,7 @@ $_default_button_c: lighten($bg_color,2%);
     color: $tc;
     outline-color: if($c != $_default_button_c, $alt_focus_border_color, $focus_border_color);
     border-color: if($c!=$_default_button_c, _border_color($c, true), $borders_color); //tint if not default button color
-    background-image: image(lighten($c, 7%));
+    background-image: image(lighten($c, 5%));
     @include _shadows($_button_shadow);
   }
 

src/themes/Kali/sass/gtk4/upstream/_drawing.scss.patch

@@ -8,4 +8,4 @@
 <     background-image: if($variant == 'light', linear-gradient(to top, darken($c, 2%) 2px, $c),
 <                                               linear-gradient(to top, darken($c,1%) 2px, $c));
 ---
->     background-image: image(lighten($c, 7%));
+>     background-image: image(lighten($c, 5%));