hubspotform.js

<script>
hbspt.forms.create({
    portalId: "0000",
    formId: "aaa-bbbb-cccc",
    onFormReady: function($form){

        var input = $form.find('input[type=email]');
        input.addClass('form-control');
        input.attr('placeholder','Enter your e-mail address');

        // Get rid of labels we don't whant them
        $form.find('label').remove();

        // Style the submit button
        $form.find('.actions').addClass('subscribe-submit form-group clearfix mb-0');
        var submit = $form.find('input[type=submit]');
        submit.addClass('btn btn-primary btn-square float-left');

    }
});
</script>