I would love to see the ability to modify the css in both of these.. because it becomes a task to design so much in these programs then have to finish the design in another. i would like the ability to set a div to 100vh for full screen backgrounds

Case, have you tried setting the min height for your div to 100vh? This should set it to be full height for your background image.

Yes, Jeff is correct, viewport units can be specified in the latest versions of both Bootstrap Builder and Foundation Framer
The Wave Weapons theme uses a height of 100vh for the full screen background.

http://bob.coffeecup.com/storage/forums/100-vh.png

Agreed on built-in editor! It is on our list but no ETA...we're still a small team so timelines for features like that are hard to plan for. Getting more people on our apps would certainly help to speed things up, please share what these apps can do everybody