Change the focused border color of a Wpf textbox when it GotFocus()

Question

What I want: to change the border color to yellow when any textbox has focus.

What I tried:

                      
        
        

          

            
            

              
              

            
    


                                 
              
            
                          
    

        
         

                验证码
                

                  
                
                

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