title: Display a warning message with a specific CSS format
body: <p>I saw the dialog as the picture below,</p>
  
  <p><a href="https://i.stack.imgur.com/bhxQa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bhxQa.png" alt="enter image description here"></a></p>
  
  <p>That is an warning message for erroneous MAC address format after the input text submitted. I would like to verify the input immediately not after it is submitted. Where can I find this css style?</p>