How to add CSS to Form?

Indeed go to the form > actions > embed code and add the lines from the example as well if they are not there:

<!--[if lte IE 8]>
<script charset="utf-8" type="text/javascript" src="//js.hsforms.net/forms/v2-legacy.js"></script>
<![endif]-->
<script charset="utf-8" type="text/javascript" src="//js.hsforms.net/forms/v2.js"></script>
<script>
 hbspt.forms.create({
	portalId: "#",
	formId: "#",
 submitButtonClass: '#',
 css: ' ',
 cssClass: '#',
});
</script>

Portal and form Id are already filled in.

SubmitButtonClass: add the class of the button

css: ‘’ makes sure that the default css is disabled

cssClass: add 1 class (2 won’t work is my experience, but if you succeed please let me know).