[Core] Fix Border margin issue (#14402) Fixes #7764

* Fox Border margin issue

* Auto-format source code

---------

Co-authored-by: GitHub Actions Autoformatter <[email protected]>

src/Controls/samples/Controls.Sample/Pages/Core/BorderGalleries/BorderPage.cs

@@ -31,6 +31,8 @@ public BorderPage()
 							new BorderLayout(), Navigation),
 						GalleryBuilder.NavButton("Border Stroke options", () =>
 							new BorderStroke(), Navigation),
+						GalleryBuilder.NavButton("Border without Stroke", () =>
+							new Borderless(), Navigation),
 					}
 				}
 			};

src/Controls/samples/Controls.Sample/Pages/Core/BorderGalleries/Borderless.xaml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage 
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    x:Class="Maui.Controls.Sample.Pages.Borderless"
+    BackgroundColor="Yellow"
+    Title="Border without Stroke">
+    <ContentPage.Resources>
+        <ResourceDictionary>
+
+            <Style x:Key="BorderlessStyle" TargetType="Border">
+                <Setter Property="StrokeThickness" Value="0" />
+            </Style>
+
+        </ResourceDictionary>
+    </ContentPage.Resources>
+    <ContentPage.Content>
+        <Grid 
+            RowDefinitions="*,*" 
+            RowSpacing="0">
+            <Border 
+                Background="Pink"
+                Style="{StaticResource BorderlessStyle}" />
+            <Border 
+                Grid.Row="1" 
+                Background="Red" 
+                Style="{StaticResource BorderlessStyle}" />
+        </Grid>
+    </ContentPage.Content>
+</ContentPage>

src/Controls/samples/Controls.Sample/Pages/Core/BorderGalleries/Borderless.xaml.cs

@@ -0,0 +1,12 @@
+using Microsoft.Maui.Controls;
+
+namespace Maui.Controls.Sample.Pages
+{
+	public partial class Borderless : ContentPage
+	{
+		public Borderless()
+		{
+			InitializeComponent();
+		}
+	}
+}

src/Controls/src/Core/Border.cs

@@ -304,6 +304,8 @@ protected override void OnPropertyChanged([CallerMemberName] string? propertyNam
 				propertyName == WidthProperty.PropertyName ||
 				propertyName == StrokeShapeProperty.PropertyName)
 				Handler?.UpdateValue(nameof(IBorderStroke.Shape));
+			else if (propertyName == StrokeThicknessProperty.PropertyName)
+				UpdateStrokeShape();
 			else if (propertyName == StrokeDashArrayProperty.PropertyName)
 				Handler?.UpdateValue(nameof(IBorderStroke.StrokeDashPattern));
 		}
@@ -312,5 +314,13 @@ void OnStrokeDashArrayChanged(object? sender, NotifyCollectionChangedEventArgs e
 		{
 			Handler?.UpdateValue(nameof(IBorderStroke.StrokeDashPattern));
 		}
+
+		void UpdateStrokeShape()
+		{
+			if (StrokeShape is Shape strokeShape)
+			{
+				strokeShape.StrokeThickness = StrokeThickness;
+			}
+		}
 	}
 }