Please see the image below:

As you can see the above warning will be only shown when there is an error while inserting the data into the login form.
Now I have tried to achieve it by:

  1. Hiding the div say "warning".
  2. Use a javascript while submitting the form to check for input validation.
  3. If found any error, the hidden div "warning" will show above the form as shown as in the image.

But till now, I couldn't succeed! So please help me.
Thank you.