Try adding “pt0 pb0” (without quotation marks & no decimal points) in the “Extra class name” field. Fortunately, they have already built-in some extra classes precisely for that purpose. Try playing around with different combinations until you get the look you want. Also, if you see no changes from creating your own extra class in the “Custom CSS” box, add !important to each property and see if that does the trick. But first try without adding !important. This probably doesn’t matter but, you might also consider shortening up the names of your extra classes to something more simple like those that Ed has added. The attached image is found towards the bottom of the theme documentation. http://flexform.swiftideas.net/documentation/
Hope that is helpful