<TextBox FontSize="17" Height="26" Margin="230,150,189,0" Name="txt_Account" VerticalAlignment="Top" Foreground="Indigo" TabIndex="0" BorderThickness="1">            <TextBox.Resources>                <VisualBrush x:Key="HelpBrush" TileMode="None" Opacity="0.3" Stretch="None" AlignmentX="Left">                    <VisualBrush.Visual>                        <TextBlock FontStyle="Italic" Text="请输入用户名"/>                    </VisualBrush.Visual>                </VisualBrush>            </TextBox.Resources>            <TextBox.Style>                <Style TargetType="TextBox">                    <Style.Triggers>                        <Trigger Property="Text" Value=http://www.mamicode.com/"{x:Null}">                            <Setter Property="Background" Value=http://www.mamicode.com/"{StaticResource HelpBrush}"/>                        </Trigger>                        <Trigger Property="Text" Value=http://www.mamicode.com/"">                            <Setter Property="Background" Value=http://www.mamicode.com/"{StaticResource HelpBrush}"/>                        </Trigger>                    </Style.Triggers>                </Style>            </TextBox.Style>        </TextBox>