sourcegit/src/Resources/Styles/TextBox.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:controls="clr-namespace:SourceGit.Views.Controls">
    <ControlTemplate x:Key="Template.Validation.Tooltip" TargetType="{x:Type ToolTip}">
        <Border x:Name="Root" Margin="5,0,0,0" Opacity="0" Padding="0,0,20,20" RenderTransformOrigin="0,0">
            <Border.RenderTransform>
                <TranslateTransform x:Name="xform" X="-25" />
            </Border.RenderTransform>
            
            <Border.Effect>
                <DropShadowEffect BlurRadius="11" ShadowDepth="6" Opacity="0.4" />
            </Border.Effect>
            
            <VisualStateManager.VisualStateGroups>
                <VisualStateGroup x:Name="OpenStates">
                    <VisualStateGroup.Transitions>
                        <VisualTransition GeneratedDuration="0" />
                        <VisualTransition GeneratedDuration="0:0:0.2" To="Open">
                            <Storyboard>
                                <DoubleAnimation Duration="0:0:0.2" To="0" Storyboard.TargetProperty="X" Storyboard.TargetName="xform">
                                    <DoubleAnimation.EasingFunction>
                                        <BackEase Amplitude=".3" EasingMode="EaseOut" />
                                    </DoubleAnimation.EasingFunction>
                                </DoubleAnimation>
                                <DoubleAnimation Duration="0:0:0.2" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root" />
                            </Storyboard>
                        </VisualTransition>
                    </VisualStateGroup.Transitions>
                    <VisualState x:Name="Closed">
                        <Storyboard>
                            <DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root" />
                        </Storyboard>
                    </VisualState>
                    <VisualState x:Name="Open">
                        <Storyboard>
                            <DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="X" Storyboard.TargetName="xform" />
                            <DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root" />
                        </Storyboard>
                    </VisualState>
                </VisualStateGroup>
            </VisualStateManager.VisualStateGroups>
            
            <Border Background="#FFDC000C" BorderThickness="1" BorderBrush="#FFBC000C">
                <TextBlock Foreground="White" MaxWidth="250" Margin="8,4,8,4" TextWrapping="Wrap" Text="{Binding [0].ErrorContent}" UseLayoutRounding="false" />
            </Border>
        </Border>
    </ControlTemplate>

    <ControlTemplate x:Key="Template.Validation.Error">
        <AdornedElementPlaceholder x:Name="Target">
            <Border BorderBrush="#FFDB000C" BorderThickness="1" x:Name="root">
                <ToolTipService.ToolTip>
                    <ToolTip x:Name="validationTooltip" 
                            Placement="Right" 
                            PlacementTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
                            Template="{StaticResource Template.Validation.Tooltip}"
                            Style="{x:Null}"/>
                </ToolTipService.ToolTip>
                <Grid Background="Transparent" HorizontalAlignment="Right" VerticalAlignment="Top">
                    <Path Width="10" Height="10" Data="M 1,0 L8,0 L8,7 z" Fill="#FFDC000C"/>
                </Grid>
            </Border>
        </AdornedElementPlaceholder>

        <ControlTemplate.Triggers>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding ElementName=Target, Path=AdornedElement.IsKeyboardFocusWithin, Mode=OneWay}" Value="True" />
                    <Condition Binding="{Binding ElementName=Target, Path=AdornedElement.(Validation.HasError), Mode=OneWay}" Value="True" />
                </MultiDataTrigger.Conditions>
                <Setter TargetName="validationTooltip" Property="IsOpen" Value="True"/>
            </MultiDataTrigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>
    
    <Style x:Key="Style.TextBox" TargetType="{x:Type TextBox}">
        <Setter Property="SnapsToDevicePixels" Value="True"/>
        <Setter Property="OverridesDefaultStyle" Value="True"/>
        <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
        <Setter Property="VerticalAlignment" Value="Center"/>
        <Setter Property="VerticalContentAlignment" Value="Center"/>
        <Setter Property="Foreground" Value="{DynamicResource Brush.FG1}"/>
        <Setter Property="CaretBrush" Value="{DynamicResource Brush.FG1}"/>
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="BorderBrush" Value="{DynamicResource Brush.Border1}"/>
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="Validation.ErrorTemplate" Value="{StaticResource Template.Validation.Error}"/>
        <Setter Property="ContextMenu">
            <Setter.Value>
                <ContextMenu>
                    <MenuItem Command="ApplicationCommands.Copy" />
                    <MenuItem Command="ApplicationCommands.Cut" />
                    <MenuItem Command="ApplicationCommands.Paste" />
                </ContextMenu>
            </Setter.Value>
        </Setter>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TextBox}">
                    <Border 
                        x:Name="Border" 
                        Background="{TemplateBinding Background}"
                        SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        BorderBrush="{TemplateBinding BorderBrush}">
                        <ScrollViewer 
                            x:Name="PART_ContentHost"
                            Margin="{TemplateBinding Padding}"
                            VerticalAlignment="Center"
                            Background="Transparent"
                            BorderThickness="0"
                            IsTabStop="False"
                            CanContentScroll="True"
                            SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                    </Border>
                        
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="true">
                            <Setter TargetName="Border" Property="BorderBrush" Value="{DynamicResource Brush.Accent1}"/>
                        </Trigger>
                        <Trigger Property="AcceptsReturn" Value="True">
                            <Setter TargetName="PART_ContentHost" Property="VerticalAlignment" Value="Top"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style TargetType="{x:Type TextBox}" BasedOn="{StaticResource Style.TextBox}"/>
    <Style TargetType="{x:Type controls:TextEdit}" BasedOn="{StaticResource Style.TextBox}"/>
</ResourceDictionary>