When I have a empty required field in a modal form the modal closes when I Submit the form and click on the error message. All other entered data is lost.

Is there a way to use a solution like the e-mail formatting example you have but just for checking an empty field and add a css class to it instead of showing up the pop-up window with the error message?

Can you please provide a link to your page, where we can check this?

I send you the link by email

You need to run the "close/hide modal" behavior with the behaviors "when the action is successfully executed", not as you currently have it on button onclick.

Ok thanks a lot.