FYI, I created a client library with the reset css that was applied to the form and it looked like it did a decent reset on all the objects in the form. Note that if you will need to apply this on and off in crx though as the touch ui editor won't work after this is applied so add it at runtime or edit your template to only add the CSS at runtime.
I'd probably approach this with a 'browser reset' type of approach where you have an intermediary reset that is applied to your form CSS prior to your css being added. Much like the browser resets that are out here but adapted to your forms.
What's the framework that you're using for your site pages that you'd like to have the forms adapt to?
Would be great if it was possible in future versions of AEM Forms to remove the default styling altogether. Although good for demo purposes, for production code where client's have exact expectations of style, the default css only gets in the way. Can someone query this with the dev team and see if it can be put in as a feature please?