Yes, you may use CSS code to style Caspio Form Elements. Please check the following forum post for your reference: JS Guide: Caspio Form Elements.
Also, you can use native Caspio Styles and modify elements to your needs.
Unfortunately, it is not possible to use Bootstrap classes in your DataPage, because Caspio classes have higher priority. But you can definitely use Bootstrap to create your HTML pages for the site where you are going to embed Caspio DataPages.
Hope this helps!