App.xaml

<Application x:Class="PasswordHoarder.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:PasswordHoarder"
             xmlns:controls="clr-namespace:PasswordHoarder.Views.Controls"
             xmlns:converters="clr-namespace:PasswordHoarder.Converters"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <converters:DateTimeToStringConverter x:Key="DateTimeToStringConverter"/>
        <converters:IsExpiredConverter x:Key="IsExpiredConverter"/> 
        <Style x:Key="ShowButton" TargetType="{x:Type Button}" BasedOn="{StaticResource {x:Type Button}}">
            <Setter Property="Background">
                <Setter.Value>
                    <ImageBrush ImageSource="/PasswordHoarder;component/Resources/eyeclosed.png"/>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <Trigger Property="IsPressed" Value="True">
                    <Setter Property="Background">
                        <Setter.Value>
                            <ImageBrush ImageSource="/PasswordHoarder;component/Resources/eyeopened.png"/>
                        </Setter.Value>
                    </Setter>
                </Trigger>
            </Style.Triggers>
        </Style>

        <Style x:Key="PlaceHolder" TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TextBox}">
                        <Grid>
                            <TextBox Text="{Binding Path=Text,
                                                RelativeSource={RelativeSource TemplatedParent}, 
                                                Mode=TwoWay,
                                                UpdateSourceTrigger=PropertyChanged}"
                                     x:Name="textSource" 
                                     Background="Transparent" 
                                     Panel.ZIndex="2" />
                            <TextBox Text="{TemplateBinding Tag}" Padding="10,0,0,0" Background="{TemplateBinding Background}" Panel.ZIndex="1">
                                <TextBox.Style>
                                    <Style TargetType="{x:Type TextBox}">
                                        <Setter Property="Foreground" Value="Transparent"/>
                                        <Style.Triggers>
                                            <DataTrigger Binding="{Binding Path=Text, Source={x:Reference textSource}}" Value="">
                                                <Setter Property="Foreground" Value="LightGray"/>
                                            </DataTrigger>
                                        </Style.Triggers>
                                    </Style>
                                </TextBox.Style>
                            </TextBox>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Application.Resources>
</Application>