Global styles in WPF

I'm learning how to use styles in WPF and according to information I found on the net, if I define style this way (with target type):

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style  TargetType="{x:Type Button}">
        <Setter Property="Background" Value="Black"/>
    </Style>
</ResourceDictionary>

...this style will be applied for all buttons in my application. However it seems that my buttons remain the same. In main window I added resource dictionary to resources collection and I inserted a couple of buttons, however my buttons look the same all the time. Here is the code for main window:

<Window x:Class="MCTSTrainingChapter1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="GridResources.xaml"/>
                <ResourceDictionary Source="ButtonResources.xaml"/>
            </ResourceDictionary.MergedDictionaries>开发者_运维知识库;
        </ResourceDictionary>
    </Window.Resources>

    <DockPanel >
        <ToolBar DockPanel.Dock="Top" Height="26" Name="toolBar1"  >
            <Button x:Name="btnBold"  Click="Button_Click">Bold</Button>
            <Button Click="Button_Click_1">Italic</Button>
            <Slider Name="slider1" Minimum="2" Maximum="72" Width="100" ValueChanged="slider1_ValueChanged"></Slider>
        </ToolBar>
        <Grid Name="grid1" Background="{StaticResource GridBackgroundBrush}">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="100"/>
                <ColumnDefinition Width="5"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <ListBox Grid.Column="0" Name="listBox1" SelectionChanged="listBox1_SelectionChanged" />
            <GridSplitter Grid.Column="1" Margin="0" Width="5" HorizontalAlignment="Left"/>
            <RichTextBox Grid.Column="2" Name="richTextBox1"/>
        </Grid>

    </DockPanel>
</Window>

Why isn't the Button style applied?

As per the answer to this question: Setting toolbar button sizes using a Style

The ToolBar is applying its own style to the button. This style can be accessed by the resource key ToolBar.ButtonStyleKey. Set up your Style with that key, rather than just Targeting the Button type, and you'll be set:

<Style x:Key="{x:Static ToolBar.ButtonStyleKey}" TargetType="Button">
    <Setter Property="Width" Value="100" />
</Style>

There is already an answer involving a global style, if you want to explicitly define your style for each button (perhaps in the future of your project) you would want to name the style:

<Style x:Key="buttonStyleOne" TargetType="{x:Type Button}">
    <Setter Property="Background" Value="Black"/>
</Style>

and then apply it to a button you want to use the style via:

<Button Style="{DynamicResource buttonStyleOne}">Content!</Button>