Proportional StatusBar

   
    
<Window x:Class="MenusAndToolbars.ProportionalStatusBar"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="ProportionalStatusBar" Height="300" Width="300">
    <Grid>
      <Grid.RowDefinitions>
        <RowDefinition></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
      </Grid.RowDefinitions>

      <StatusBar Grid.Row="1">
        <StatusBar.ItemsPanel>
          <ItemsPanelTemplate>
            <Grid>
              <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"></ColumnDefinition>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
              </Grid.ColumnDefinitions>              
            </Grid>
          </ItemsPanelTemplate>
        </StatusBar.ItemsPanel>
        <TextBlock>Left Side</TextBlock>
        <StatusBarItem Grid.Column="1">
          <TextBlock>Right Side</TextBlock>
        </StatusBarItem>
      </StatusBar>
    </Grid>
  </Window>