Hi adrian,
The css class you are using belong to the default styling of gravity forms. However, the new HTML output is no longer a hack within the li elements of gravity forms but creates proper HTML fieldsets. Because of this, the gf_left_half and gf_right_half classes only apply to actual input field and not to the fieldsets. So this means you will have to add some custom css yourself in order to make the fieldsets go left or right.
So .gform_wrapper .top_label li.gfield.gf_left_half
will need to be
.gform_wrapper .gf_left_half
or add your own custom classes to the fieldsets.
Cheers, Harro