如何让按钮的IsFocused或GotFocus/LostFocus触发按钮模板中元素的动画

<Button Content="Click Me">
    <Button.Template>
        <ControlTemplate TargetType="Button">
            <Grid>
                <!-- 按钮模板中的其他元素 -->
                <TextBlock Text="Hello World" x:Name="textBlock" />
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="IsFocused" Value="True">
                    <Trigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation Storyboard.TargetName="textBlock"
                                                 Storyboard.TargetProperty="Opacity"
                                                 To="0.5" Duration="0:0:0.5" />
                            </Storyboard>
                        </BeginStoryboard>
                    </Trigger.EnterActions>
                    <Trigger.ExitActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation Storyboard.TargetName="textBlock"
                                                 Storyboard.TargetProperty="Opacity"
                                                 To="1" Duration="0:0:0.5" />
                            </Storyboard>
                        </BeginStoryboard>
                    </Trigger.ExitActions>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
    </Button.Template>
</Button>