Bootstrap 3 styles for Gravity Forms, make sure that in Forms > Settings you have Output CSS set to No and Output HTML5 set to Yes

new_gist_file.css

.gform_wrapper ul {
  padding-left: 0;
  list-style: none; }

.gform_wrapper li {
  margin-bottom: 15px; }

.gform_wrapper form {
  margin-bottom: 0; }

.gform_wrapper .gfield_required {
  padding-left: 1px;
  color: #b94a48; }

.ginput_container input, .ginput_container select, .ginput_container textarea {
  display: block;
  width: 100%;
  height: 34px;
  padding: 6px 12px;
  font-size: 14px;
  line-height: 1.428571429;
  color: #555;
  vertical-align: middle;
  background-color: #fff;
  border: 1px solid #ccc;
  border-radius: 4px;
  -webkit-box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075);
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075);
  -webkit-transition: border-color ease-in-out .15s, box-shadow ease-in-out .15s;
  transition: border-color ease-in-out .15s, box-shadow ease-in-out .15s; }

.ginput_container input:-moz-placeholder, .ginput_container select:-moz-placeholder, .ginput_container textarea:-moz-placeholder {
  color: #999; }

.ginput_container input::-moz-placeholder, .ginput_container select::-moz-placeholder, .ginput_container textarea::-moz-placeholder {
  color: #999; }

.ginput_container input:-ms-input-placeholder, .ginput_container select:-ms-input-placeholder, .ginput_container textarea:-ms-input-placeholder {
  color: #999; }

.ginput_container input::-webkit-input-placeholder, .ginput_container select::-webkit-input-placeholder, .ginput_container textarea::-webkit-input-placeholder {
  color: #999; }

.ginput_container input:focus, .ginput_container select:focus, .ginput_container textarea:focus {
  border-color: #66afe9;
  outline: 0;
  -webkit-box-shadow: inset 0 1px 1px rgba(0, 0, 0, .075), 0 0 8px rgba(102, 175, 233, 0.6);
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, .075), 0 0 8px rgba(102, 175, 233, 0.6); }

.ginput_container input[disabled], .ginput_container select[disabled], .ginput_container textarea[disabled], .ginput_container input[readonly], .ginput_container select[readonly], .ginput_container textarea[readonly], fieldset[disabled] .ginput_container input, fieldset[disabled] .ginput_container select, fieldset[disabled] .ginput_container textarea {
  cursor: not-allowed;
  background-color: #eee; }

textarea.ginput_container input, textarea.ginput_container select, textarea.ginput_container textarea {
  height: auto; }

.ginput_container textarea {
  height: auto; }

.gform_button {
  display: inline-block;
  padding: 6px 12px;
  margin-bottom: 0;
  font-size: 14px;
  font-weight: normal;
  line-height: 1.428571429;
  text-align: center;
  vertical-align: middle;
  cursor: pointer;
  border: 1px solid transparent;
  border-radius: 4px;
  white-space: nowrap;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  -o-user-select: none;
  user-select: none;
  color: #fff;
  background-color: #428bca;
  border-color: #357ebd; }

.gform_button:focus {
  outline: thin dotted #333;
  outline: 5px auto -webkit-focus-ring-color;
  outline-offset: -2px; }

.gform_button:hover, .gform_button:focus {
  color: #333;
  text-decoration: none; }

.gform_button:active, .gform_button.active {
  outline: 0;
  background-image: none;
  -webkit-box-shadow: inset 0 3px 5px rgba(0, 0, 0, 0.125);
  box-shadow: inset 0 3px 5px rgba(0, 0, 0, 0.125); }

.gform_button.disabled, .gform_button[disabled], fieldset[disabled] .gform_button {
  cursor: not-allowed;
  pointer-events: none;
  opacity: .65;
  filter: alpha(opacity=65);
  -webkit-box-shadow: none;
  box-shadow: none; }

.gform_button:hover, .gform_button:focus, .gform_button:active, .gform_button.active, .open .dropdown-toggle.gform_button {
  color: #fff;
  background-color: #3276b1;
  border-color: #285e8e; }

.gform_button:active, .gform_button.active, .open .dropdown-toggle.gform_button {
  background-image: none; }

.gform_button.disabled, .gform_button[disabled], fieldset[disabled] .gform_button, .gform_button.disabled:hover, .gform_button[disabled]:hover, fieldset[disabled] .gform_button:hover, .gform_button.disabled:focus, .gform_button[disabled]:focus, fieldset[disabled] .gform_button:focus, .gform_button.disabled:active, .gform_button[disabled]:active, fieldset[disabled] .gform_button:active, .gform_button.disabled.active, .gform_button[disabled].active, fieldset[disabled] .gform_button.active {
  background-color: #428bca;
  border-color: #357ebd; }

.gform_wrapper .gfield_error .gfield_label {
  color: #b94a48; }

.gform_wrapper .gfield_error input, .gform_wrapper .gfield_error select, .gform_wrapper .gfield_error textarea {
  border-color: #eed3d7;
  background-color: #f2dede;
  color: #b94a48; }

.gform_wrapper .gfield_error input:focus, .gform_wrapper .gfield_error select:focus, .gform_wrapper .gfield_error textarea:focus {
  border-color: #b94a48;
  outline: 0;
  -webkit-box-shadow: inset 0 1px 1px rgba(0, 0, 0, .075), 0 0 8px rgba(185, 74, 72, 0.6);
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, .075), 0 0 8px rgba(185, 74, 72, 0.6); }

.validation_error {
  padding: 15px;
  margin-bottom: 20px;
  border: 1px solid transparent;
  border-radius: 4px;
  background-color: #f2dede;
  border-color: #eed3d7;
  color: #b94a48; }

.validation_error h4 {
  margin-top: 0;
  color: inherit; }

.validation_error .alert-link {
  font-weight: bold; }

.validation_error>p, .validation_error>ul {
  margin-bottom: 0; }

.validation_error>p+p {
  margin-top: 5px; }

.validation_error hr {
  border-top-color: #e6c1c7; }

.validation_error .alert-link {
  color: #953b39; }

#gforms_confirmation_message {
  padding: 15px;
  margin-bottom: 20px;
  border: 1px solid transparent;
  border-radius: 4px; }

#gforms_confirmation_message h4 {
  margin-top: 0;
  color: inherit; }

#gforms_confirmation_message .alert-link {
  font-weight: bold; }

#gforms_confirmation_message>p, #gforms_confirmation_message>ul {
  margin-bottom: 0; }

#gforms_confirmation_message>p+p {
  margin-top: 5px; }

.gallery-row {
  padding: 15px 0; }

.aligncenter {
  display: block;
  margin: 0 auto; }

.alignleft {
  float: left; }

.alignright {
  float: right; }

figure.alignnone {
  margin-left: 0;
  margin-right: 0; }

Perfect, thanks.

Incredible!

Awesome! This helps so much. Thank you.

This is awesome, but I found a few things that need to be added for the date-picker and labels.

.ui-widget {
  background: white;
  padding: 10px;
  border-radius: 5px;
  border: 1px solid #ccc;
  box-shadow: 0 3px 5px rgba(0, 0, 0, 0.125);
}

.ui-widget td {
  text-align: center;
  padding: 3px 0;
  /*border: 1px solid #ccc;*/
}
.ui-widget td a {
  padding: 3px 8px;
}

.ui-datepicker-next {
  float: right;
}

.gform_wrapper label {
  font-weight: normal;
  font-style: italic;
}

.gform_wrapper .gfield_label {
  display: inline-block;
  max-width: 100%;
  margin-bottom: 5px;
  font-weight: bold;
  font-style: normal;
}

Many thanks!