<Grid
  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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="d"
  Height="450" Width="800">

  <Viewbox HorizontalAlignment="Right" VerticalAlignment="Bottom">
      <Grid x:Name="RootGrid" Width="800" Height="450" Background="WhiteSmoke">
          <StackPanel>
            <StackPanel.Resources>
              <ControlTemplate x:Key="btnTemplate" TargetType="Button">
                <Grid x:Name="RootGrid" Background="Cyan">
                  <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
                </Grid>
              </ControlTemplate>
              <Style TargetType="Button">
                <Setter Property="Template" Value="{StaticResource btnTemplate}"/>
              </Style>
            </StackPanel.Resources>
            <Button Width="200" Height="100" Content="Button A"/>
            <Button Width="200" Height="100" Content="Button B" Margin="0,10"/>
          </StackPanel>
      </Grid>
  </Viewbox>
</Grid>