Style Gravity Forms with Bootstrap 3 Taken from: http://roots.io/style-gravity-forms-with-bootstrap/

gravityforms.less

/**
 * Gravity Forms styles with Bootstrap 3 mixins
 *
 * GF settings: 
 * - Output CSS = No
 * - Output HTML5 = Yes
 */

.gform_wrapper ul {
  .list-unstyled();
}
.gform_wrapper li {
  .form-group();
}
.gform_wrapper form {
  margin-bottom: 0;
}
.gform_wrapper .gfield_label {
}
.gform_wrapper .gfield_required {
  padding-left: 1px;
  color: @state-danger-text;
}
.ginput_container input,
.ginput_container select,
.ginput_container textarea {
  .form-control();
}
.ginput_container textarea {
  height: auto;
}
.gform_button {
  .btn();
  .btn-primary();
}
.gform_wrapper .gfield_error {
  .gfield_label {
    color: @state-danger-text;
  }
  input,
  select,
  textarea {
    border-color: @alert-danger-border;
    background-color: @alert-danger-bg;
    color: @alert-danger-text;
    .form-control-focus(@alert-danger-text);
  }
}
.validation_error {
  .alert();
  .alert-danger();
}
#gforms_confirmation_message {
  .alert();
}