WPF Change Style of all TextBoxes in Grid

Dear All

Hi everyone,

I am using control template to change all the textboxes' style in specific Grid, all textboxes outside the Grid will have different style
I works fine with the following code, but I need one more enhancement

I would like to change a textbox's borderbrush to red when a button click, however, since I am set the color to Blue in style, the code textBox1.BorderBrush = Brushes.Red; is not working

How to modify the controlTemplate that normal style is Blue border and when a button is clicked, the code textBox1.BorderBrush = Brushes.Red; can change the border to Red?

Thanks
Ivan

Here are my codes:

XAML:

 
 
 
 
   
 
 
 
   
 
       

Code Behind:

  private void button1_Click(object sender, RoutedEventArgs e)
  {
  textBox1.BorderBrush = Brushes.Red;
  }