You are missing the <Setter.Value>
<Style ...>
<Setter Property="...">
<Setter.Value>
<LinearGradientBrush />
</Setter.Value>
</Setter>
</Style>
You are missing the <Setter.Value>
<Style ...>
<Setter Property="...">
<Setter.Value>
<LinearGradientBrush />
</Setter.Value>
</Setter>
</Style>