Bootstrap 4 floating labels with an .input-group

I'm trying to achieve floating labels with an .input-group in Bootstrap 4.6

Floating labels without the input group are working. The code is copied from official bootstrap 4.6 example. You can test the behaviour on this page: https://getbootstrap.com/docs/4.0/examples/floating-labels/

Now what I'm trying to achieve is to have that kind of floating labels with my input-group. My test page example looks like this:

The floating labels CSS is as follows:

.form-label-group {
  position: relative;
  margin-bottom: 1rem;
}

.form-label-group input,
.form-label-group label {
  height: 3.125rem;
  padding: .75rem;
}

.form-label-group label {
  position: absolute;
  top: 0;
  left: 0;
  display: block;
  width: 100%;
  margin-bottom: 0; /* Override default `<label>` margin */
  line-height: 1.5;
  color: #495057;
  pointer-events: none;
  cursor: text; /* Match the input under the label */
  border: 1px solid transparent;
  border-radius: .25rem;
  transition: all .1s ease-in-out;
}

.form-label-group input::-webkit-input-placeholder {
  color: transparent;
}

.form-label-group input::-moz-placeholder {
  color: transparent;
}

.form-label-group input:-ms-input-placeholder {
  color: transparent;
}

.form-label-group input::-ms-input-placeholder {
  color: transparent;
}

.form-label-group input::placeholder {
  color: transparent;
}

.form-label-group input:not(:-moz-placeholder-shown) {
  padding-top: 1.25rem;
  padding-bottom: .25rem;
}

.form-label-group input:not(:-ms-input-placeholder) {
  padding-top: 1.25rem;
  padding-bottom: .25rem;
}

.form-label-group input:not(:placeholder-shown) {
  padding-top: 1.25rem;
  padding-bottom: .25rem;
}

.form-label-group input:not(:-moz-placeholder-shown) ~ label {
  padding-top: .25rem;
  padding-bottom: .25rem;
  font-size: 12px;
  color: #777;
}

.form-label-group input:not(:-ms-input-placeholder) ~ label {
  padding-top: .25rem;
  padding-bottom: .25rem;
  font-size: 12px;
  color: #777;
}

.form-label-group input:not(:placeholder-shown) ~ label {
  padding-top: .25rem;
  padding-bottom: .25rem;
  font-size: 12px;
  color: #777;
}

.form-label-group input:-webkit-autofill ~ label {
  padding-top: .25rem;
  padding-bottom: .25rem;
  font-size: 12px;
  color: #777;
}

/* Fallback for Edge
-------------------------------------------------- */
@supports (-ms-ime-align: auto) {
  .form-label-group {
    display: -ms-flexbox;
    display: flex;
    -ms-flex-direction: column-reverse;
    flex-direction: column-reverse;
  }

  .form-label-group label {
    position: static;
  }

  .form-label-group input::-ms-input-placeholder {
    color: #777;
  }
}

My HTML for the page is this:

<!-- Receiver -->
                        <div class="col-lg-4">
                            <div class="form-section">
                                <span class="section-title">Destinatario</span>
                                <div class="section-fields">
                                    <div class="form-label-group">
                                        <input type="text" class="form-control" id="destination-country"
                                               name="destination-country" placeholder="Paese">
                                        <label for="destination-country">Paese</label>
                                    </div>
                                    <div class="form-label-group">
                                        <input type="text" class="form-control" id="destination-place"
                                               name="destination-place" placeholder="Città - Codice Postale">
                                        <label for="destination-place">Città / CAP</label>
                                    </div>
                                </div>
                            </div>
                        </div>

                        <!-- Package -->
                        <div class="col-lg-4">
                            <div class="form-section">
                                <span class="section-title">Pacco</span>
                                <div class="section-fields">
                                    <div class="form-group input-group">
                                        <input type="text" class="form-control" id="pack-width"
                                               name="pack-width" placeholder="Larghezza">
                                        <input type="text" class="form-control" id="pack-height"
                                               name="pack-height" placeholder="Altezza">
                                        <input type="text" class="form-control" id="pack-length"
                                               name="pack-length" placeholder="Lunghezza">
                                    </div>
                                </div>
                            </div>
                        </div>

As far as I can see, .input-group class doesn't support a <label> tag linked to the specific input, it relies just on placeholders. The floating labels relies on a label tag linked to the input to actually show something. I still didn't managed to find a way to make those labels show.