Div not showing after select

For some reason, I can display boxes and all, but everytime I try to display a DIV after a select has been chosen, nothing happens… Please advice.

JS:

$(document).ready(function () {
            var divs = document.getElementById('showRef');
            divs.style.display = 'none';
            $('.selRef').on('change', function () {

                var refValid = (this.value == "Yes");
                $(txtWeek).prop('required', refValid);
                if (refValid) {
                    divs.style.display = 'block';
                }
                else {
                    divs.style.display = 'none';
                }
            })
        });

ASP:

                                    <div class="col-md-12">
                                        <div class="input-group">
                                            <select id='selRef'
                                            required runat="server" clientidmode="Static" class="form-control selRef">
                                            <option value="No" selected>No</option>
                                            <option value="Yes">Yes</option>
                                        </select>
                                        </div>
                                    </div>
                                </div>

                            </div>
                            <div id="showRef" runat="server">
                            <div class="row mt-3">
                    ....

Everytime I click or change the dropdownvalue, nothing happens…