选中时如何在UWP中显示按钮上的边框

<Style x:Key="CustomButtonStyle" TargetType="Button">
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="Foreground" Value="{ThemeResource SystemControlForegroundBaseHighBrush}"/>
    <Setter Property="BorderBrush" Value="{ThemeResource SystemControlForegroundTransparentBrush}"/>
    <Setter Property="BorderThickness" Value="2"/>
    <Setter Property="Padding" Value="8,4"/>
    <Setter Property="HorizontalAlignment" Value="Left"/>
    <Setter Property="VerticalAlignment" Value="Center"/>
    <Setter Property="FontFamily" Value="{ThemeResource ContentControlThemeFontFamily}"/>
    <Setter Property="FontWeight" Value="SemiBold"/>
    <Setter Property="FontSize" Value="{ThemeResource ControlContentThemeFontSize}"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Button">
                <Grid>
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup x:Name="CommonStates">
                            <VisualState x:Name="Normal"/>
                            <VisualState x:Name="PointerOver">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Border" Storyboard.TargetProperty="BorderBrush">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="Pressed">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Border" Storyboard.TargetProperty="Background">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundBaseMediumLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlForegroundBaseHighBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Border" Storyboard.TargetProperty="BorderBrush">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlForegroundBaseMediumHighBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="Disabled">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Border" Storyboard.TargetProperty="Background">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundBaseLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Border" Storyboard.TargetProperty="BorderBrush">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="BorderBrush">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledTransparentBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <Border x:Name="Border"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Background="{TemplateBinding Background}"
                            Margin="3">
                        <ContentPresenter x:Name="ContentPresenter"
                                          Content="{TemplateBinding Content}"
                                          ContentTransitions="{TemplateBinding ContentTransitions}"
                                          ContentTemplate="{TemplateBinding ContentTemplate}"
                                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                          VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                          Padding="{TemplateBinding Padding}"/>
                    </Border>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Button Style="{StaticResource CustomButtonStyle}" Content="按钮" />