silviomoreto bootstrap-select change tick sign to checkbox

I am modifying another person's code Here is the HTML

   <div class="day-wrap flo-le">
                            <span class="day-txt">A 타입 : </span>
                                <div class="row" style="display:inline-block;margin-left:5px">
                                <div class="col-xs-5" style="display:inline-block">
                                    <div class="form-group" style="display:inline-block">
                                        <select id="select_type_a" class="selectpicker" data-style="btn-new" multiple data-actions-box="true" data-tick-icon="" style="height:45px;"> <!-- multiple data-actions-box="true"-->
                                            {% for _row in list_a %}                                                                                                                   <!-- checkbox error disappeared-->
                                            <option selected>{{ _row.dst_columns_name }}</option>
                                            {% endfor %}
                                        </select>
                                   </div>
                                </div>
                            </div>
                        </div>

Here is the CSS code

.bootstrap-select.btn-group.show-tick .dropdown-menu li.selected a span.check-mark { // Place tick signs to the left
  position: absolute;
  display: inline-block;
  left: 5px; //changed from right:15
  margin-top: 0;
  }
/*.bootstrap-select.btn-group.show-tick .dropdown-menu li.selected a span.check-mark::after {
  border-style: solid;
 }*/

I am using silviomoreto bootstrap-select to allow multiple selection. I would like to change this tick sign to a checkbox like element. The commented out CSS code is my attempt to do it. However, it only draws a box for a selected element. If it is possible, I would like to draw a box before a drop down list element is selected. I understand there is another option for this checkbox selection. However, I am afraid there will be a hidden conflict if I do so since I just got into the project in the middle. Does any of you have any idea on it? this HTML has Flask Jinja code. Sorry for it if it bothers you.