wpf 设置ComboBox下拉框背景颜色

你可以使用ComboBox的样式来更改下拉框的背景颜色。以下是一个示例，将ComboBox的下拉框背景颜色设置为灰色：

<ComboBox>
    <ComboBox.Resources>
        <Style TargetType="{x:Type ComboBox}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ComboBox}">
                        <Grid>
                            <ToggleButton 
                                Name="ToggleButton" 
                                ClickMode="Press"
                                Focusable="False"
                                IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}"
                                Grid.Column="2" 
                                Grid.Row="0" 
                                Style="{StaticResource ComboBoxToggleButton}"
                                Background="Gray"/>
                            <ContentPresenter
                                Name="ContentSite"
                                IsHitTestVisible="False" 
                                Content="{TemplateBinding SelectionBoxItem}"
                                ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
                                ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
                                Margin="3,3,23,3"
                                VerticalAlignment="Center"
                                HorizontalAlignment="Left" />
                            <TextBox x:Name="PART_EditableTextBox"
                                     Style="{x:Null}" 
                                     Template="{StaticResource ComboBoxTextBox}" 
                                     HorizontalAlignment="Left" 
                                     VerticalAlignment="Bottom" 
                                     Margin="3,3,23,3"
                                     Focusable="True" 
                                     Background="Transparent"
                                     Visibility="Hidden"
                                     IsReadOnly="{TemplateBinding IsReadOnly}"/>
                            <Popup 
                                Name="Popup"
                                Placement="Bottom"
                                IsOpen="{TemplateBinding IsDropDownOpen}"
                                AllowsTransparency="True" 
                                Focusable="False"
                                PopupAnimation="Slide">
                                <Grid 
                                    Name="DropDown"
                                    SnapsToDevicePixels="True"                
                                    MinWidth="{TemplateBinding ActualWidth}"
                                    MaxHeight="{TemplateBinding MaxDropDownHeight}">
                                    <Border 
                                        x:Name="DropDownBorder"
                                        Background="White"
                                        BorderThickness="1"
                                        BorderBrush="Black"/>
                                    <ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
                                        <StackPanel IsItemsHost="True" />
                                    </ScrollViewer>
                                </Grid>
                            </Popup>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsEnabled" Value="False">
                                <Setter TargetName="PART_EditableTextBox" Property="Foreground" Value="DimGray"/>
                            </Trigger>
                            <Trigger Property="IsGrouping" Value="True">
                                <Setter Property="ScrollViewer.CanContentScroll" Value="False"/>
                            </Trigger>
                            <Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="True">
                                <Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4"/>
                                <Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0"/>
                            </Trigger>
                            <Trigger Property="IsEditable"
                                     Value="True">
                                <Setter Property="IsTabStop" Value="False"/>
                                <Setter TargetName="PART_EditableTextBox" Property="Visibility"    Value="Visible"/>
                                <Setter TargetName="ContentSite" Property="Visibility" Value="Hidden"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </ComboBox.Resources>
    <ComboBoxItem>Item 1</ComboBoxItem>
    <ComboBoxItem>Item 2</ComboBoxItem>
    <ComboBoxItem>Item 3</ComboBoxItem>
</ComboBox>

在这个示例中，我们将ComboBox的模板更改为一个包含ToggleButton、ContentPresenter、TextBox和Popup的Grid。ToggleButton用于展开和收起下拉框，ContentPresenter用于显示当前选择的项，TextBox用于允许用户编辑文本，Popup用于显示下拉框中的项。

我们可以使用Background属性将ToggleButton的背景颜色设置为灰色。在这个示例中，我们还更改了其他控件的样式和模板，以便它们与ToggleButton的颜色相匹配。

请注意，这只是一个示例，你可以根据你的需要自定义ComboBox的外观和行为。