CustomMessageBox.xaml

<Window x:Class="efcClient.Windows.CustomMessageBox"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="CustomMessageBox" MaxHeight="150" MaxWidth="300" ResizeMode="NoResize"
        WindowStartupLocation="CenterScreen" ScrollViewer.VerticalScrollBarVisibility="Auto" ShowInTaskbar="False" WindowStyle="ToolWindow"
        Loaded="Window_Loaded">
    <Grid>
        <ScrollViewer VerticalScrollBarVisibility="Auto" MaxHeight="80" HorizontalAlignment="Left" VerticalAlignment="Top">
            <TextBlock Name="messageBlock" HorizontalAlignment="Left" Margin="10,5,0,0" TextWrapping="Wrap" Text="TextBlock" VerticalAlignment="Top"/>
        </ScrollViewer>
        <StackPanel Margin="0,5,20,10" HorizontalAlignment="Right" Orientation="Horizontal" VerticalAlignment="Bottom">
            <Button Content="Button1" Name="button1" HorizontalAlignment="Right" Margin="0,0,10,0" VerticalAlignment="Top" MinWidth="75" Click="button1_Click"/>
            <Button Content="Button2" Name="button2" HorizontalAlignment="Right" Margin="0,0,0,0" VerticalAlignment="Top" MinWidth="75" Click="button2_Click"/>
        </StackPanel>        
    </Grid>
</Window>