scroll view: Allow styling via panel

skins/material3/QskMaterial3Skin.cpp

@@ -757,6 +757,8 @@ void Editor::setupScrollView()
     using A = QskAspect;
     using Q = QskScrollView;
 
+    setGradient( Q::Panel, m_pal.background );
+
     setGradient( Q::Viewport, m_pal.secondaryContainer );
 
     for ( auto subControl : { Q::HorizontalScrollBar, Q::VerticalScrollBar } )

src/controls/QskScrollViewSkinlet.cpp

@@ -41,7 +41,7 @@ static void qskAlignedHandle( qreal start, qreal end,
 QskScrollViewSkinlet::QskScrollViewSkinlet( QskSkin* skin )
     : Inherited( skin )
 {
-    setNodeRoles( { ViewportRole, ContentsRootRole,
+    setNodeRoles( { PanelRole, ViewportRole, ContentsRootRole,
         HorizontalScrollBarRole, HorizontalScrollHandleRole,
         VerticalScrollBarRole, VerticalScrollHandleRole } );
 }
@@ -93,6 +93,10 @@ QSGNode* QskScrollViewSkinlet::updateSubNode(
 
     switch ( nodeRole )
     {
+        case PanelRole:
+        {
+            return updateBoxNode( skinnable, node, QskScrollView::Panel );
+        }
         case ViewportRole:
         {
             return updateBoxNode( skinnable, node, QskScrollView::Viewport );

src/controls/QskScrollViewSkinlet.h

@@ -19,6 +19,7 @@ class QSK_EXPORT QskScrollViewSkinlet : public QskSkinlet
   public:
     enum NodeRole
     {
+        PanelRole,
         ViewportRole,
         ContentsRootRole,