WPF

<FontFamily x:Key="Font.Family.Default">Segoe UI</FontFamily>
<sys:Double x:Key="Font.Size.Header1">18</sys:Double>
<sys:Double x:Key="Font.Size.Header2">16</sys:Double>
<sys:Double x:Key="Font.Size.Header3">14</sys:Double>
<sys:Double x:Key="Font.Size.Normal">12</sys:Double>

<SolidColorBrush x:Key="TextBlock.Static.Background" Color="Transparent"/>
<SolidColorBrush x:Key="TextBlock.Static.Foreground" Color="DarkGray"/>

<Style x:Key="ControlBase" TargetType="{x:Type Control}">

    <Setter Property="Control.FontSize" Value="{StaticResource Font.Size.Normal}"/>
    <Setter Property="Control.FontFamily" Value="{StaticResource Font.Family.Default}"/>
    <Setter Property="Control.HorizontalAlignment" Value="Center"/>
    <Setter Property="Control.VerticalAlignment" Value="Center"/>

</Style>

<Style TargetType="{x:Type TextBlock}"
        BasedOn="{StaticResource ControlBase}">

    <Setter Property="Background" Value="{StaticResource TextBlock.Static.Background}"/>
    <Setter Property="Foreground" Value="{StaticResource TextBlock.Static.Foreground}"/>

</Style>

<TextBlock Grid.Row="0" 
            Grid.Column="0"
            Text="Test"
            Margin="22,0,0,0"/>

System.Windows.Markup.XamlParseException
  Message='Initialization of 'System.Windows.Controls.TextBlock' threw an exception.' Line number '56' and line position '20'.

    Inner Exception 1:
    InvalidOperationException: Can only base on a Style with target type that is base type 'TextBlock'.

<Style TargetType="TextBlock">

    <Setter Property="Foreground" Value="{DynamicResource textForegroundBrush}"/>
    <Setter Property="FontSize" Value="14"/>

</Style>

<Window.Resources>

    <Style x:Key="headerTextStyle" 
            TargetType="TextBox">

        <Setter Property="FontSize" Value="24"/>

    </Style>

</Window.Resources>

using ...

namespace Gewicht
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public string[] dbFile = { @"H:\Daten\C#WPF\Gewicht\GewichtDaten.xml", @"H:\Daten\C#WPF\Gewicht\GewichtDaten.xsd" };
        public DataTable dbDataTbl = new DataTable();

        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            if (!System.IO.File.Exists(dbFile[0]) | !System.IO.File.Exists(dbFile[1]))
                {
                SystemSounds.Beep.Play();
                MessageBox.Show("Die Datei" + Environment.NewLine + "   " + dbFile[0] + Environment.NewLine + "und/oder" + Environment.NewLine + "   " + dbFile[1] + Environment.NewLine + "fehlt." + Environment.NewLine + "Das Programm wird beendet.", "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
                Environment.Exit(0);
            }
            DataGrid1.CanUserAddRows = false;
            DataGrid1.CanUserDeleteRows = false;
            OpenData();
        }


        private void DataGrid1_CellEditEnding(object sender, DataGridCellEditEndingEventArgs e)
        {
            // edit
            // ... ???????????????????????? ...
        }


        private void OpenData()
        {
            // open data

            dbDataTbl.Columns.Clear();
            dbDataTbl.Rows.Clear();
            dbDataTbl = new DataTable("ich");
            dbDataTbl.ReadXmlSchema(dbFile[1]);
            dbDataTbl.ReadXml(dbFile[0]);
            // DataGrid
            DataSet dataSet = new DataSet();
            dataSet.ReadXml(dbFile[0]);
            DataView dataView = new DataView(dataSet.Tables[0]);
            DataGrid1.ItemsSource = dataView;
            // format columns
            Style style = new Style();               // creates object of style class   
            style.TargetType = typeof(DataGridCell); // sets target type as DataGrid cell
            Setter setter = new Setter();            // create objects of setter class   
            setter.Property = DataGridCell.ForegroundProperty;
            setter.Value = Brushes.LightGray;
            style.Setters.Add(setter);
            DataGrid1.Columns[0].CellStyle = style;
            style = new Style();
            setter = new Setter();
            setter.Property = DataGridCell.HorizontalContentAlignmentProperty;
            setter.Value = HorizontalAlignment.Right;
            DataGrid1.Columns[2].CellStyle = style;
        }

    }
}

<DrawingImage x:Key="FindIcon"/>
<DrawingImage x:Key="SearchIcon"/>

<Image Source="{StaticResource FindIcon}"/>
<Image Source="{StaticResource SearchIcon}"/>

<Image Source="{Binding ChooseIcon}"/>

public DrawingImage ChooseIcon
{
    get
    {
        if (useFindIcon)
        {
            return ???; // how to reference the static resource "FindIcon"
        }
        else if (useSearchIcon)
        {
            return ???;// how to reference the static resource "SearchIcon"
        }
    }
}