How do I customize the style of a tooltip that gets shown ONLY on the CheckBoxes in my Window?

Nest the tooltip’s style within the checkbox’s style as follows:

    <Window.Resources>  
        <Style TargetType='CheckBox'>   
            <Style.Resources>  
                <Style TargetType='ToolTip'>   
                    <Setter Property='Background' Value='Red'/>   
                </Style>  
            </Style.Resources>  
            <Setter Property='FontSize' Value='14'/>   
        </Style>  
    </Window.Resources>  
    <Grid>  
        <CheckBox ToolTip='Sample ToolTip!'>Sample CheckBox</CheckBox>  
    </Grid>