title: How to change TextBox border color and Style while typing?
body: <p>I'm writing a C# programming which has couple of textboxes which give some information from the user. I have a "Submit" button to save the entered information.
   I want this textbox work like this:
  A. When there is no information entered, by pressing the Submit button, a thick red border shown around the textbox.
  B. when the user is been noticed, and try to enter some information in the corresponding textbox, after a certain number of letters (for example after entering at least 4 letters), the border style of the textbox will be switched to the regular style!</p>
  
  <p>I will be appreciated if you could help me! 
  I searched a lot for TextBox border color but I couldn't find anything helpful.</p>