Within Form Builder, on the Setup Page, you can choose the Theme of the site or form you are building.  Next to the Theme drop down menu, you will see a Preview Theme hyperlink.  Clicking this will show you a side by side view of the structure of the theme as well as a sample site.

Below you will find the images for the available themes.

Aspen Theme:

 Galway Theme:

Generic Theme:

Minimal Theme:

Odelay Theme:

St. John’s Theme:

 Entity Theme: (optimized for use within a Personalization or an <iframe> tag)