CustomMessageBox.xaml

<Window x:Class="Google_Bookmarks_Manager_for_GPOs.CustomMessageBox"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
        Title="CustomMessageBox" 
        WindowStartupLocation="CenterOwner"
        ResizeMode="NoResize"
        SizeToContent="WidthAndHeight"
        TextElement.Foreground="{DynamicResource MaterialDesign.Brush.Foreground}"
        Background="{DynamicResource MaterialDesign.Brush.Background}"
        TextElement.FontWeight="Regular"
        TextElement.FontSize="12"
        FontFamily="{materialDesign:MaterialDesignFont}"
        TextOptions.TextFormattingMode="Ideal"
        TextOptions.TextRenderingMode="Auto">

    <Border CornerRadius="8" BorderBrush="{DynamicResource MaterialDesignDivider}" BorderThickness="1" Padding="16">
        <StackPanel>
            <TextBlock x:Name="MessageTextBlock" TextWrapping="Wrap" Margin="0,0,0,16" FontSize="16" TextAlignment="Center" Style="{DynamicResource MaterialDesignBody1TextBlock}"/>

            <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
                <Button x:Name="OKButton" Content="OK" Width="75" Margin="5" Click="OKButton_Click" Style="{DynamicResource MaterialDesignRaisedButton}"/>
                <Button x:Name="CancelButton" Content="Cancel" Width="75" Margin="5" Click="CancelButton_Click" Style="{DynamicResource MaterialDesignRaisedButton}"/>
            </StackPanel>
        </StackPanel>
    </Border>
</Window>