title: How to make custom border for a Form without Title Bar?
body: <p>I have a form without Title bar, but I want my Form still have border, like this:</p>
  
  <p><img src="https://i.stack.imgur.com/REvwD.png" alt="enter image description here"></p>
  
  <p>Currently, I used a textbox then send it to back, my Form have 1px-border. I build tiny app, so I dont want write long code to draw border. Is there any simple way to do this: <strong>I want my Form have simple black-3px-border, but without Title Bar???</strong></p>
  
  <p>Language: C#</p>