Sidebars: add support for Adw.NavigationSplitView (#1327)

* Sidebars: add support for Adw.NavigationSplitView

* Update stylesheet.appdata.xml.in

Author: danirabbit

data/stylesheet.appdata.xml.in

@@ -24,6 +24,12 @@
 
   <releases>
     <release version="8.2.2" date="2025-07-07" urgency="medium">
+      <description>
+        <p>Improve support for LibAdwaita widgets:</p>
+        <ul>
+          <li>Add Adw.NavigationSplitView styles</li>
+        </ul>
+      </description>
       <issues>
         <issue url="https://github.com/elementary/stylesheet/issues/1244">The primary text in Granite.HeaderLabel misaligned when placed in Gtk.Popover</issue>
       </issues>

src/gtk-4.0/widgets/_sidebars.scss

@@ -15,6 +15,7 @@
     }
 }
 
+.sidebar-pane,
 .sidebar,
 .sidebar.view,
 .source-list {
@@ -29,6 +30,7 @@
     }
 }
 
+.sidebar-pane,
 .sidebar {
     &:dir(ltr) {
         border-right: 1px solid #{'@menu_separator'};
@@ -56,6 +58,11 @@
     }
 }
 
+// Nested Adw.NavigationSplitView
+.sidebar-pane .content-pane {
+    background: bg_color(1);
+}
+
 placessidebar.frame,
 placessidebar viewport.frame {
     border: none;