diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml b/samples/ControlCatalog/Pages/DataGridPage.xaml
index d1742c12b7..7b86bba6a9 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml
@@ -18,7 +18,7 @@
     </StackPanel>
     <TabControl Grid.Row="1">
       <TabItem Header="DataGrid">
-        <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True">
+        <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
           <DataGrid.Columns>
             <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" />
             <DataGridTextColumn Header="Region" Binding="{Binding Region}" Width="4*" />
diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
index b8f63cf3e3..fea18aa5da 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
@@ -13,7 +13,7 @@ namespace ControlCatalog.Pages
             this.InitializeComponent();
             var dg1 = this.FindControl<DataGrid>("dataGrid1");
             dg1.IsReadOnly = true;
-
+            dg1.LoadingRow += Dg1_LoadingRow;
             var collectionView1 = new DataGridCollectionView(Countries.All);
             //collectionView.GroupDescriptions.Add(new PathGroupDescription("Region"));
 
@@ -44,6 +44,11 @@ namespace ControlCatalog.Pages
             addButton.Click += (a, b) => collectionView3.AddNew();
         }
 
+        private void Dg1_LoadingRow(object sender, DataGridRowEventArgs e)
+        {
+            e.Row.Header = e.Row.GetIndex() + 1;
+        }
+
         private void InitializeComponent()
         {
             AvaloniaXamlLoader.Load(this);
diff --git a/src/Avalonia.Controls.DataGrid/DataGridCell.cs b/src/Avalonia.Controls.DataGrid/DataGridCell.cs
index 99efc5743d..e5fbfa1a81 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridCell.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridCell.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Controls
         private Rectangle _rightGridLine;
         private DataGridColumn _owningColumn;
 
-        bool _isValid;
+        bool _isValid = true;
 
         public static readonly DirectProperty<DataGridCell, bool> IsValidProperty =
             AvaloniaProperty.RegisterDirect<DataGridCell, bool>(
@@ -191,7 +191,7 @@ namespace Avalonia.Controls
 
             PseudoClasses.Set(":edited", IsEdited);
 
-            // PseudoClasses.Set(":invalid", !IsValid);
+            PseudoClasses.Set(":invalid", !IsValid);
         }
 
         // Makes sure the right gridline has the proper stroke and visibility. If lastVisibleColumn is specified, the 
diff --git a/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs b/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
index e504fe73a8..0833247439 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
@@ -334,7 +334,7 @@ namespace Avalonia.Controls
         {
             if (_headerElement != null && OwningGrid != null)
             {
-                _headerElement.IsVisible = OwningGrid.AreColumnHeadersVisible;
+                _headerElement.IsVisible = OwningGrid.AreRowHeadersVisible;
             }
         }
 
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
index 85c1af10ef..94a6274a26 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
@@ -7,12 +7,10 @@
                      Color="#3F4346" />
     <SolidColorBrush x:Key="DisabledVisualElementBackground"
                      Color="#8CFFFFFF" />
-    <SolidColorBrush x:Key="InvalidBrush"
-                     Color="#FFFF00" />
     <SolidColorBrush x:Key="FillerGridLinesBrush"
                      Color="Transparent" />
     <StaticResource x:Key="ScrollBarsSeparatorBackground"
-                    ResourceKey="SystemControlPageBackgroundChromeLowBrush" />
+                    ResourceKey="SystemChromeLowColor" />
     <StaticResource x:Key="DataGridColumnHeaderForegroundBrush"
                     ResourceKey="SystemControlForegroundBaseMediumBrush" />
     <StaticResource x:Key="DataGridColumnHeaderBackgroundColor"
@@ -90,7 +88,7 @@
     <StaticResource x:Key="DataGridRowGroupHeaderForegroundBrush"
                     ResourceKey="SystemControlForegroundBaseHighBrush" />
     <StaticResource x:Key="DataGridRowInvalidBrush"
-                    ResourceKey="InvalidBrush" />
+                    ResourceKey="SystemControlErrorTextForegroundBrush" />
     <StaticResource x:Key="DataGridCellBackgroundBrush"
                     ResourceKey="SystemControlTransparentBrush" />
     <StaticResource x:Key="DataGridCellFocusVisualPrimaryBrush"
@@ -98,7 +96,7 @@
     <StaticResource x:Key="DataGridCellFocusVisualSecondaryBrush"
                     ResourceKey="SystemControlFocusVisualSecondaryBrush" />
     <StaticResource x:Key="DataGridCellInvalidBrush"
-                    ResourceKey="InvalidBrush" />
+                    ResourceKey="SystemControlErrorTextForegroundBrush" />
   </Styles.Resources>
 
   <Style Selector="DataGridCell">
@@ -433,7 +431,7 @@
     <Setter Property="MinHeight" Value="32" />
     <Setter Property="Template">
       <ControlTemplate>
-        <DataGridFrozenGrid Name="Root"
+        <DataGridFrozenGrid Name="PART_Root"
                             MinHeight="{TemplateBinding MinHeight}"
                             ColumnDefinitions="Auto,Auto,Auto,Auto,*"
                             RowDefinitions="*,Auto">
@@ -492,11 +490,11 @@
                        StrokeThickness="1" />
           </Grid>
 
-          <DataGridRowHeader Name="RowHeader"
+          <DataGridRowHeader Name="PART_RowHeader"
                              Grid.RowSpan="2"
                              DataGridFrozenGrid.IsFrozen="True" />
 
-          <Rectangle x:Name="BottomGridLine"
+          <Rectangle x:Name="PART_BottomGridLine"
                      Grid.Row="1"
                      Grid.ColumnSpan="5"
                      Height="1" />
@@ -533,13 +531,13 @@
     <Setter Property="Stretch" Value="UniformToFill" />
   </Style>
 
-  <Style Selector="DataGridRowGroupHeader /template/ DataGridFrozenGrid#Root">
+  <Style Selector="DataGridRowGroupHeader /template/ DataGridFrozenGrid#PART_Root">
     <Setter Property="Background" Value="{Binding $parent[DataGridRowGroupHeader].Background}" />
   </Style>
-  <Style Selector="DataGridRowGroupHeader:pointerover /template/ DataGridFrozenGrid#Root">
+  <Style Selector="DataGridRowGroupHeader:pointerover /template/ DataGridFrozenGrid#PART_Root">
     <Setter Property="Background" Value="{DynamicResource DataGridRowGroupHeaderHoveredBackgroundBrush}" />
   </Style>
-  <Style Selector="DataGridRowGroupHeader:pressed /template/ DataGridFrozenGrid#Root">
+  <Style Selector="DataGridRowGroupHeader:pressed /template/ DataGridFrozenGrid#PART_Root">
     <Setter Property="Background" Value="{DynamicResource DataGridRowGroupHeaderPressedBackgroundBrush}" />
   </Style>