gravityforms-bootstrap4

gforms_styles.css

  .btn > .caret, .gform_button > .caret,
  .dropup > .btn > .caret,
  .dropup > .gform_button > .caret {
    border-top-color: #000 !important;
  }

.gform_fields {
  padding-left: 0;
  list-style: none;
  margin-left: -15px;
  margin-right: -15px;
}

.gform_fields::after {
  content: "";
  display: table;
  clear: both;
}

.form-control, .gform_fields input, .gform_fields select, .gform_fields textarea {
  display: block;
  width: 100%;
  padding: 0.5rem 0.75rem;
  font-size: 1rem;
  line-height: 1.25;
  color: #55595c;
  background-color: #fff;
  background-image: none;
  -webkit-background-clip: padding-box;
          background-clip: padding-box;
  border: 1px solid rgba(0, 0, 0, 0.15);
  border-radius: 0.25rem;
}

.gform_fields input::-ms-expand, .gform_fields select::-ms-expand, .gform_fields textarea::-ms-expand {
  background-color: transparent;
  border: 0;
}

.gform_fields input:focus, .gform_fields select:focus, .gform_fields textarea:focus {
  color: #55595c;
  background-color: #fff;
  border-color: #66afe9;
  outline: none;
}

.gform_fields input::-webkit-input-placeholder, .gform_fields select::-webkit-input-placeholder, .gform_fields textarea::-webkit-input-placeholder {
  color: #999;
  opacity: 1;
}

.gform_fields input::-moz-placeholder, .gform_fields select::-moz-placeholder, .gform_fields textarea::-moz-placeholder {
  color: #999;
  opacity: 1;
}

.gform_fields input:-ms-input-placeholder, .gform_fields select:-ms-input-placeholder, .gform_fields textarea:-ms-input-placeholder {
  color: #999;
  opacity: 1;
}

.gform_fields input::placeholder, .gform_fields select::placeholder, .gform_fields textarea::placeholder {
  color: #999;
  opacity: 1;
}

.gform_fields input:disabled, .gform_fields select:disabled, .gform_fields textarea:disabled, .gform_fields input[readonly], .gform_fields select[readonly], .gform_fields textarea[readonly] {
  background-color: #eceeef;
  opacity: 1;
}

.gform_fields input:disabled, .gform_fields select:disabled, .gform_fields textarea:disabled {
  cursor: not-allowed;
}

.gform_fields select:not([size]):not([multiple]) {
  height: 2.5rem;
}

.gform_fields select:focus::-ms-value {
  color: #55595c;
  background-color: #fff;
}

.gform_fields .input-group-sm > input.form-control-static, .gform_fields .input-group-sm > select.form-control-static, .gform_fields .input-group-sm > textarea.form-control-static,
.gform_fields .input-group-lg > input.form-control-static, .gform_fields .input-group-lg > select.form-control-static, .gform_fields .input-group-lg > textarea.form-control-static {
	padding-right: 0;
	padding-left: 0;
}

 .gform_fields .input-group-sm > input, .gform_fields .input-group-sm > select, .gform_fields .input-group-sm > textarea {
 	padding: 0.25rem 0.5rem;
 	font-size: 0.875rem;
 	border-radius: 0.2rem;
 }

 .gform_fields .input-group-sm > select:not([size]):not([multiple]) {
 	height: 1.8125rem;
 }

 .gform_fields .input-group-lg > input, .gform_fields .input-group-lg > select, .gform_fields .input-group-lg > textarea {
 	  padding: 0.75rem 1.5rem;
 	  font-size: 1.25rem;
 	  border-radius: 0.3rem;
 }

 .gform_fields .input-group-lg > select:not([size]):not([multiple]) {
 	height: 3.166667rem;
 }

  .gform_wrapper ul.gfield_radio li, .gform_wrapper ul.gfield_checkbox li {
  position: relative;
  display: block;
  margin-bottom: 0.75rem;
}

.gform_wrapper ul.gfield_radio li + .form-check, .gform_wrapper ul.gfield_checkbox li + .form-check, .gform_wrapper ul.gfield_radio .form-check + li, .gform_wrapper ul.gfield_radio li + li, .gform_wrapper ul.gfield_checkbox .form-check + li, .gform_wrapper ul.gfield_checkbox li + li {
  margin-top: -.25rem;
}

.gform_wrapper ul.gfield_radio li.disabled .form-check-label, .gform_wrapper ul.gfield_checkbox li.disabled .form-check-label {
  color: #818a91;
  cursor: not-allowed;
}

.gform_fields input, .gform_fields .has-success input, .has-success .gform_fields select, .gform_fields .has-success select, .has-success .gform_fields textarea, .gform_fields .has-success textarea {
  border-color: #5cb85c;
}

.gform_fields input, .gform_fields .has-warning input, .has-warning .gform_fields select, .gform_fields .has-warning select, .has-warning .gform_fields textarea, .gform_fields .has-warning textarea {
  border-color: #f0ad4e;
}

.gform_fields input, .gform_fields .has-danger input, .has-danger .gform_fields select, .gform_fields .has-danger select, .has-danger .gform_fields textarea, .gform_fields .has-danger textarea {
  border-color: #d9534f;
}

.gform_button {
  display: inline-block;
  font-weight: normal;
  line-height: 1.25;
  text-align: center;
  white-space: nowrap;
  vertical-align: middle;
  cursor: pointer;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  border: 1px solid transparent;
  padding: 0.5rem 1rem;
  font-size: 1rem;
  border-radius: 0.25rem;
}

.gform_button:focus, .btn.focus, .focus.gform_button, .gform_button:active:focus .gform_button:active.focus, .active.gform_button:focus, .active.focus.gform_button {
  outline: 5px auto -webkit-focus-ring-color;
  outline-offset: -2px;
}

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

.focus.gform_button {
  text-decoration: none;
}

.gform_button:active, .active.gform_button {
  background-image: none;
  outline: 0;
}

.disabled.gform_button, .gform_button:disabled {
  cursor: not-allowed;
  opacity: .65;
}

a.btn.disabled, a.disabled.gform_button,
fieldset[disabled] a.btn,
fieldset[disabled] a.gform_button {
  pointer-events: none;
}

gfield_description, .validation_error, .validation_message {
  padding: 1rem;
  margin-bottom: 1rem;
  border: 1px solid transparent;
  border-radius: 0.25rem;
}

.validation_message {
  background-color: #dff0d8;
  border-color: #d0e9c6;
  color: #3c763d;
}

.validation_message hr {
  border-top-color: #c1e2b3;
}

.validation_message .alert-link {
  color: #2b542c;
}

.gform_fields textarea {
  height: auto;
}

.gfield_required {
  color: #a94442;
}

.gform_validation_container {
  display: none;
}

.gfield_error .ginput_container {
  margin-bottom: 10px;
}

@media (min-width: 544px) {
.form-inline .gform_fields input, .gform_fields .form-inline input, .form-inline .gform_fields select, .gform_fields .form-inline select, .form-inline .gform_fields textarea, .gform_fields .form-inline textarea {
    display: inline-block;
    width: auto;
    vertical-align: middle;
  }

  .form-inline .input-group .gform_fields input, .gform_fields
  .form-inline .input-group input,
  .form-inline .input-group .gform_fields select, .gform_fields
  .form-inline .input-group select,
  .form-inline .input-group .gform_fields textarea, .gform_fields
  .form-inline .input-group textarea {
    width: auto;
  }
  .form-inline .input-group > .form-control, .form-inline .gform_fields .input-group > input, .gform_fields .form-inline .input-group > input, .form-inline .gform_fields .input-group > select, .gform_fields .form-inline .input-group > select, .form-inline .gform_fields .input-group > textarea, .gform_fields .form-inline .input-group > textarea {
    width: 100%;
  }

  .gform_wrapper ul.gfield_radio li, .gform_wrapper ul.gfield_radio .form-inline li, .form-inline .gform_wrapper ul.gfield_checkbox li, .gform_wrapper ul.gfield_checkbox .form-inline li {
    display: inline-block;
    margin-top: 0;
    margin-bottom: 0;
    vertical-align: middle;
  }

}

Thank you for this! Such a time saver. Few notes:

• Alert styles will probably need to be altered on a case by case basis
• Input heights should be set/debugged for each browser.

Cheers!