Wrap form on modular page in a div?

I have a form on a modular page. My theme has no form.html.twig template, and neither does the Quark theme. It seems that the templates in the form plugin folder are being used. However, I would like to simply wrap the whole section with the form and its headline in a div. How do I do that? Can I just copy one of the form templates from the plugin, change the path of the extend reference, and put the div in there? I'm unsure about how to do this, many thanks for your help!