GridLayout

<Grid>
   <Grid.ColumnDefinitions>
       <ColumnDefinition Width="Auto">
       <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
       <RowDefinition Height="Auto" />
     </Grid.RowDefinitions>
      <Label Grid.Column="0" Grid.Row="0" Content="Eingabe" Margin="20 20 20 0" Foreground="Tomato"  />
      <TextBox Grid.Column="1" Grid.Row="0" Grid.ColumnSpan="2" Name="tInput" Text="abc" Margin="20 20 20 0" />
</Grid>