WPF -重写子控件/内部控件上继承的样式

<Style TargetType="Button">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Button">
                <Grid>
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <ContentPresenter HorizontalAlignment="Center"
                                          VerticalAlignment="Center"/>
                    </Border>
                    <Rectangle x:Name="CustomRectangle"
                               Fill="Red"
                               Width="50"
                               Height="50"
                               Visibility="Collapsed"/>
                </Grid>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter TargetName="CustomRectangle" Property="Visibility" Value="Visible"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>