How to make the background of TextBox transparent in uwp?

Question

I'm trying to make a uwp application with dark theme.

But after I change the theme from light to dark, when I type in the textbox, the background of the textbox is white, rather than black.

So how can I change the background of the textbox when the textbox is in edit mode?

The codes of mine which takes no effect:

<Style x:Key="TextBoxStyle" TargetType="TextBox">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="TextBox">
                <Border Name="TextBoxBorder" CornerRadius="10" BorderThickness="2" BorderBrush="Gray">
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup>
                            <VisualState x:Name="Normal" />
                            <VisualState x:Name="Focused">
                                <VisualState.Setters>
                                    <Setter Target="TextBox.Background" Value="Black" />
                                    <Setter Target="TextBox.Foreground" Value="White" />
                                </VisualState.Setters>
                            </VisualState>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <TextBox x:Name="TextBox" BorderThickness="0" BorderBrush="Transparent" 
                             Background="Transparent"
                             Margin="2"/>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

When I start to type in the textbox of my app, the background is white.

When I start to type in the textbox of System App -- Mail, the background remains black.

Answer 1

Here is the Style Template that I created in Blend from Existing Template. Below is the result on focus.

<Style x:Key="TextBoxStyleBlack" TargetType="TextBox">
    <Setter Property="MinWidth" Value="{ThemeResource TextControlThemeMinWidth}"/>
    <Setter Property="MinHeight" Value="{ThemeResource TextControlThemeMinHeight}"/>
    <Setter Property="Foreground" Value="{ThemeResource SystemControlForegroundBaseHighBrush}"/>
    <Setter Property="Background" Value="{ThemeResource SystemControlBackgroundAltHighBrush}"/>
    <Setter Property="BorderBrush" Value="{ThemeResource SystemControlForegroundChromeDisabledLowBrush}"/>
    <Setter Property="SelectionHighlightColor" Value="{ThemeResource SystemControlHighlightAccentBrush}"/>
    <Setter Property="BorderThickness" Value="{ThemeResource TextControlBorderThemeThickness}"/>
    <Setter Property="FontFamily" Value="{ThemeResource ContentControlThemeFontFamily}"/>
    <Setter Property="FontSize" Value="{ThemeResource ControlContentThemeFontSize}"/>
    <Setter Property="ScrollViewer.HorizontalScrollMode" Value="Auto"/>
    <Setter Property="ScrollViewer.VerticalScrollMode" Value="Auto"/>
    <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Hidden"/>
    <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Hidden"/>
    <Setter Property="ScrollViewer.IsDeferredScrollingEnabled" Value="False"/>
    <Setter Property="Padding" Value="{ThemeResource TextControlThemePadding}"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="TextBox">
                <Grid>
                    <Grid.Resources>
                        <Style x:Name="DeleteButtonStyle" TargetType="Button">
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate TargetType="Button">
                                        <Grid x:Name="ButtonLayoutGrid" BorderBrush="{ThemeResource TextBoxButtonBorderThemeBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{ThemeResource TextBoxButtonBackgroundThemeBrush}">
                                            <VisualStateManager.VisualStateGroups>
                                                <VisualStateGroup x:Name="CommonStates">
                                                    <VisualState x:Name="Normal"/>
                                                    <VisualState x:Name="PointerOver">
                                                        <Storyboard>
                                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="GlyphElement">
                                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/>
                                                            </ObjectAnimationUsingKeyFrames>
                                                        </Storyboard>
                                                    </VisualState>
                                                    <VisualState x:Name="Pressed">
                                                        <Storyboard>
                                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="ButtonLayoutGrid">
                                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/>
                                                            </ObjectAnimationUsingKeyFrames>
                                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="GlyphElement">
                                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltChromeWhiteBrush}"/>
                                                            </ObjectAnimationUsingKeyFrames>
                                                        </Storyboard>
                                                    </VisualState>
                                                    <VisualState x:Name="Disabled">
                                                        <Storyboard>
                                                            <DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="ButtonLayoutGrid"/>
                                                        </Storyboard>
                                                    </VisualState>
                                                </VisualStateGroup>
                                            </VisualStateManager.VisualStateGroups>
                                            <TextBlock x:Name="GlyphElement" AutomationProperties.AccessibilityView="Raw" Foreground="{ThemeResource SystemControlForegroundChromeBlackMediumBrush}" FontStyle="Normal" FontSize="12" FontFamily="{ThemeResource SymbolThemeFontFamily}" HorizontalAlignment="Center" Text="&#xE10A;" VerticalAlignment="Center"/>
                                        </Grid>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </Grid.Resources>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*"/>
                        <ColumnDefinition Width="Auto"/>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto"/>
                        <RowDefinition Height="*"/>
                    </Grid.RowDefinitions>
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup x:Name="CommonStates">
                            <VisualState x:Name="Disabled">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="HeaderContentPresenter">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseMediumLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BackgroundElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledTransparentBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BorderElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundBaseLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledChromeDisabledLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="PlaceholderTextContentPresenter">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledChromeDisabledLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="Normal"/>
                            <VisualState x:Name="PointerOver">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightChromeAltLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource TextControlBackgroundHoverOpacity}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="Focused">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="PlaceholderTextContentPresenter">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlPageTextChromeBlackMediumLowBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    **<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BackgroundElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ApplicationPageBackgroundThemeBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>**
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource TextControlBackgroundFocusedOpacity}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    **<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ApplicationForegroundThemeBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>**
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="RequestedTheme" Storyboard.TargetName="ContentElement">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="Light"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                        </VisualStateGroup>
                        <VisualStateGroup x:Name="ButtonStates">
                            <VisualState x:Name="ButtonVisible">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Visibility" Storyboard.TargetName="DeleteButton">
                                        <DiscreteObjectKeyFrame KeyTime="0">
                                            <DiscreteObjectKeyFrame.Value>
                                                <Visibility>Visible</Visibility>
                                            </DiscreteObjectKeyFrame.Value>
                                        </DiscreteObjectKeyFrame>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="ButtonCollapsed"/>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <Border x:Name="BackgroundElement" Background="{TemplateBinding Background}" Grid.ColumnSpan="2" Margin="{TemplateBinding BorderThickness}" Opacity="{ThemeResource TextControlBackgroundRestOpacity}" Grid.Row="1" Grid.RowSpan="1"/>
                    <Border x:Name="BorderElement" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="2" Grid.Row="1" Grid.RowSpan="1"/>
                    <ContentPresenter x:Name="HeaderContentPresenter" Grid.ColumnSpan="2" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" Foreground="{ThemeResource SystemControlForegroundBaseHighBrush}" FontWeight="Normal" Margin="0,0,0,8" Grid.Row="0" Visibility="Collapsed" x:DeferLoadStrategy="Lazy"/>
                    <ScrollViewer x:Name="ContentElement" AutomationProperties.AccessibilityView="Raw" HorizontalScrollMode="{TemplateBinding ScrollViewer.HorizontalScrollMode}" HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}" IsTabStop="False" IsHorizontalRailEnabled="{TemplateBinding ScrollViewer.IsHorizontalRailEnabled}" IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}" IsDeferredScrollingEnabled="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}" Margin="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.Row="1" VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}" VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}" ZoomMode="Disabled"/>
                    <ContentControl x:Name="PlaceholderTextContentPresenter" Grid.ColumnSpan="2" Content="{TemplateBinding PlaceholderText}" Foreground="{ThemeResource SystemControlPageTextBaseMediumBrush}" IsHitTestVisible="False" IsTabStop="False" Margin="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.Row="1" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"/>
                    <Button x:Name="DeleteButton" BorderThickness="{TemplateBinding BorderThickness}" Grid.Column="1" FontSize="{TemplateBinding FontSize}" IsTabStop="False" Margin="{ThemeResource HelperButtonThemePadding}" MinWidth="34" Grid.Row="1" Style="{StaticResource DeleteButtonStyle}" Visibility="Collapsed" VerticalAlignment="Stretch" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Look closer @ <VisualState x:Name="Focused">

You will see I changed TargetProperty Background and Foreground to respective ThemeResources

Good Luck and Happy Coding.