MainWindow.xaml

<Window
    x:Class="DesktopTool.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:DesktopTool"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="280"
    Height="450"
    AllowsTransparency="True"
    MouseMove="WindowMouseMove"
    ShowInTaskbar="False"
    Topmost="True"
    WindowStyle="None"
    mc:Ignorable="d">
    <Canvas Background="Brown">
        <TextBox
            x:Name="Message"
            Canvas.Left="20"
            Canvas.Top="40"
            Width="200"
            Height="40"
            MaxWidth="200"
            TextWrapping="WrapWithOverflow" />
        <Button
            Canvas.Left="220"
            Canvas.Top="40"
            Width="40"
            Height="40"
            Click="AddItem">
            add
        </Button>
        <Button
            Canvas.Left="220"
            Canvas.Top="10"
            Width="40"
            Height="25"
            Click="Close">
            Close
        </Button>
        <ScrollViewer
            Canvas.Left="20"
            Canvas.Top="100"
            Width="240"
            Height="320"
            MaxHeight="320"
            Background="#FF1E4363"
            VerticalScrollBarVisibility="Hidden">

            <StackPanel x:Name="List" />
        </ScrollViewer>
    </Canvas>
</Window>