MessageWindow.xaml

<Window x:Class="XColumn.MessageWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:ui="http://schemas.modernwpf.com/2019"
        Title="Title" Height="200" Width="450"
        WindowStartupLocation="CenterOwner"
        ResizeMode="NoResize"
        SizeToContent="Height"
        ui:WindowHelper.UseModernWindowStyle="True"
        Background="{DynamicResource SystemControlPageBackgroundChromeLowBrush}">
    <Grid Margin="20">
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <TextBlock Name="MessageTextBlock" Text="Message" TextWrapping="Wrap" Margin="0,0,0,20"
                   Foreground="{DynamicResource SystemControlPageTextBaseHighBrush}"/>

        <StackPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right">
            <Button Name="YesButton" Content="はい" MinWidth="80" Padding="10,5" Margin="0,0,10,0" Click="YesButton_Click" Visibility="Collapsed"/>
            <Button Name="NoButton" Content="いいえ" MinWidth="80" Padding="10,5" Margin="0,0,10,0" Click="NoButton_Click" Visibility="Collapsed"/>
            <Button Name="OkButton" Content="OK" MinWidth="80" Padding="10,5" IsDefault="True" Click="OkButton_Click"/>
            <Button Name="CancelButton" Content="キャンセル" MinWidth="80" Padding="10,5" IsCancel="True" Click="CancelButton_Click" Visibility="Collapsed"/>
        </StackPanel>
    </Grid>
</Window>