WPF UI Close button

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid Background="Blue" >
        <Grid Background="#0101FFFF" MouseLeftButtonDown="Grid_MouseLeftButtonDown" MouseLeftButtonUp="Grid_MouseLeftButtonUp" MouseEnter="Grid_MouseEnter" MouseLeave="Grid_MouseLeave" Width="122" Height="122" RenderTransformOrigin="0.5,0.5">
            <Grid.RenderTransform>
                <RotateTransform Angle="45" />
            </Grid.RenderTransform>
            <Rectangle Name="r1" Fill="White" RadiusX="6"  RadiusY="6" Width="12"></Rectangle>
            <Rectangle  Name="r2" Fill="White" RadiusX="6"  RadiusY="6" Height="12"></Rectangle>
        </Grid>
    </Grid>
</Window>

 private void Grid_MouseEnter(object sender, MouseEventArgs e)
        {
            r1.Fill = r2.Fill = new SolidColorBrush(Colors.Red);
        }

        private void Grid_MouseLeave(object sender, MouseEventArgs e)
        {
            r1.Fill = r2.Fill = new SolidColorBrush(Colors.White );
        }

        private void Grid_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            r1.Fill = r2.Fill = new SolidColorBrush(Colors.DarkRed);
        }

        private void Grid_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            r1.Fill = r2.Fill = new SolidColorBrush(Colors.Red );
        }