Style for ellipse not working

Question

I create a style in resource dictionary file as below for silverlight app:

<Style x:Key="YesStyle" TargetType="Ellipse">
    <Setter Property="Stroke" Value="Black"/>
    <Setter Property="Height" Value="14"/>
    <Setter Property="Width" Value="14"/>
    <Setter Property="HorizontalAlignment" Value="Left"/>
    <Setter Property="Margin" Value="0,-220,0,0"/>
    <Setter Property="VerticalAlignment" Value="Top"/>
    <Setter Property="Fill">
        <Setter.Value>
            <LinearGradientBrush EndPoint="0.942,0.239" StartPoint="0.078,0.776">
                <GradientStop Color="#FFFFFFFF"/>
                <GradientStop Color="#FFFC0E06" Offset="0.035"/>
                <GradientStop Color="#FFE8EBF0" Offset="1"/>
            </LinearGradientBrush>
        </Setter.Value>
    </Setter>
</Style>

then use it in user control as below:

<Ellipse Style="{StaticResource YesStyle}" />

When run the app, nothing comes out. no error. Why?