How to make Gravity Forms Responsive (left/right )?

If your theme is responsive you most likely have a custom css file if you don't you can use this code, just declare all your responsive class defs in the @media section.

@media only screen and (min-width: 200px) and (max-width: 768px) {

  .gform_wrapper .gform_body .top_label li.gfield.gf_right_half { 
    float: left; 
    clear: left !important;
    width: 99%;
  } 

  .gform_wrapper .gform_body .top_label li.gfield.gf_left_half { 
    float: left; 
    clear: left !important;
    width: 99%;
  }

}