工程名称：WpfApp1

新建Styles文件夹；
创建“Dictionary1.xaml”的文件；

    <SolidColorBrush x:Key="MainColor">#FF000000</SolidColorBrush>

    <SolidColorBrush x:Key="MainColor1">#FFFFFFFF</SolidColorBrush>

    <Style  TargetType="Button">

        <Setter Property="Background" Value="Blue"/>

    </Style>

    <Style TargetType="TextBox">

        <Setter Property="FontFamily" Value="微软雅黑"/>

        <Setter Property="FontSize" Value="23"/>

    </Style>

    <Application.Resources>

        <ResourceDictionary>

            <ResourceDictionary.MergedDictionaries>

                <ResourceDictionary Source="pack://application:,,,/WpfApp1;component/Styles/Dictionary1.xaml"/>

            </ResourceDictionary.MergedDictionaries>

        </ResourceDictionary>

    </Application.Resources>

        <Button Content="主题颜色" Width="100" Height="40" Margin="545,82,155,328"/>

        <Button Content="主题颜色" Width="100" Height="40" Margin="545,127,155,283"/>

        <Button Content="外部样式" Width="100" Height="40" Margin="144,270,556,140" Background="{StaticResource MainColor}" Foreground="{StaticResource MainColor1}"/>