[Plugin: Form Manager] Exporting a form to a site out the WP build

My goal is this: I want to create a splash page for a new website that allows users to submit data. (Much like many websites that invite users to submit their names for beta testing.) All other content on the website would be hidden.

I’d rather make an .HTML page and import—somehow—a form handled on the WP end. The rationale is that I do not need to hack-and-slash the CSS on that one splash page, since it will look strikingly different from the regular site.

I’m using Form manager which uses shortcode [like this]. Any thoughts or suggestions would also be appreciated.