Основы WPF

<Window x:Class="WpfApp3.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Thumb, Border, Popup" 
    Height="300" 
    Width="300"
    Background="LightGray"
    >
    <TabControl>
        <!--Элемент, описывающий перемещаемую область-->
        <TabItem Header="Thumb">
            <Canvas>
                <Thumb 
                        Name="thumb1"
                        Background="Red"
                        Canvas.Left="5"
                        Canvas.Top="5"
                        Width="23"
                        Height="23"
                        DragStarted="thumb1_DragStarted"
                        DragDelta="thumb1_DragDelta" 
                        />
            </Canvas>
        </TabItem>
    
        <!--Применение рамок Border-->
        <TabItem Header="Border">
            <StackPanel>
                <Border
                        BorderThickness="3"
                        CornerRadius="0"
                        BorderBrush="Black"
                        Padding="5"
                        Margin="10"
                        Background="Violet"
                        >
                    <TextBlock HorizontalAlignment="Center">
                            Привет1
                    </TextBlock>
                </Border>
                <Border
                        BorderThickness="3"
                        CornerRadius="3"
                        BorderBrush="Black"
                        Padding="5"
                        Margin="10"
                        Background="Violet"
                        >
                    <TextBlock HorizontalAlignment="Center">
                            Привет2
                    </TextBlock>
                </Border>
                <Border
                        BorderThickness="10,1,10,1"
                        CornerRadius="10"
                        BorderBrush="Black"
                        Padding="5"
                        Margin="10"
                        Background="Violet"
                        >
                    <TextBlock HorizontalAlignment="Center">
                            Привет3
                    </TextBlock>
                </Border>
                <Border
                        BorderThickness="4,1,4,1"
                        CornerRadius="0,15,0,15"
                        BorderBrush="Black"
                        Padding="5"
                        Margin="10"
                        Background="Violet"
                        >
                    <TextBlock HorizontalAlignment="Center">
                            Привет4
                    </TextBlock>
                </Border>
            </StackPanel>
        </TabItem>
    
        <!--Применение элемента Popup-->
        <TabItem Header="Popup">
            <StackPanel>
                <Button Name="btn" Click="btn_Click">Toggle</Button>
                <Popup Name="popup"
                        PopupAnimation="Fade"
                        Placement="Mouse"
                        >
                    <Button Background="Yellow" Foreground="Red">
                        Кнопка создана в Popup
                    </Button>
                </Popup>
            </StackPanel>
        </TabItem>
    </TabControl>
</Window>

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
    
using System.Windows.Controls.Primitives;
    
namespace WpfApp3
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }
    
        protected override void OnMouseDoubleClick(MouseButtonEventArgs e)
        {
            base.OnMouseDoubleClick(e);
    
            // Возвращаем Thumb в исходное состояние
            Canvas.SetLeft(thumb1, 5);
            Canvas.SetTop(thumb1, 5);
        }
    
        double originalLeft, originalTop;
        private void thumb1_DragStarted(object sender, DragStartedEventArgs e)
        {
            originalLeft = Canvas.GetLeft(thumb1);
            originalTop = Canvas.GetTop(thumb1);
        }
    
        private void thumb1_DragDelta(object sender, DragDeltaEventArgs e)
        {
            double left = originalLeft + e.HorizontalChange;
            double top = originalTop + e.VerticalChange;
            Canvas.SetLeft(thumb1, left);
            Canvas.SetTop(thumb1, top);
            originalLeft = left;
            originalTop = top;
        }
    
        private void btn_Click(object sender, RoutedEventArgs e)
        {
            popup.IsOpen = !popup.IsOpen;
        }
    }
}