You can just copy a template from /packages/acs-templating/resources/forms and edit it. Then set the style like this:
<formtemplate id="my_form_name" style="/path/of/template/form_template_name">
If you put your new template into /packages/acs-templating/resources/forms then you will only need to put the template name in style like so:
<formtemplate id="my_form_name" style="form_template_name">
I hope it helps :)
