如何在不覆盖包的情况下在WPF中应用样式？

<Style x:Key="ButtonStyle" TargetType="Button">
    <Setter Property="Background" Value="Red"/>
    <Setter Property="Foreground" Value="White"/>
</Style>

<Style x:Key="CustomButtonStyle" TargetType="Button" BasedOn="{StaticResource ButtonStyle}">
    <Setter Property="Background" Value="Blue"/>
</Style>

<Button Content="Button 1" Style="{StaticResource ButtonStyle}"/>
<Button Content="Button 2" Style="{StaticResource CustomButtonStyle}"/>

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="ButtonStyles.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>