jquery making html checkbox appear as blinking question mark and exclamatory mark

i have created a checkbox list group from bootstrap, the code is like below:

<link href="https://www.ishtasakhi.com/assets/css/bootstrap-checkbox-radio-list-group-item.css" rel="stylesheet" />
<link href="https://www.ishtasakhi.com/assets/css/bootstrap-checkbox-radio-list-group-item.min.css" rel="stylesheet" />
<div class="list-group checkbox-list-group">
  <div style="height:45px;" class="list-group-item">&nbsp;<label><input type="checkbox"><span class="list-group-item-text"><i class="fa fa-fw"></i> Large</span></label></div>
  <div style="height:45px;" class="list-group-item">&nbsp;<label><input type="checkbox"><span class="list-group-item-text"><i class="fa fa-fw"></i> Medium</span></label></div>
</div>


  <script src="https://www.ishtasakhi.com/assets/js/jquery-plugins.js"></script>

as you can see I have included my jquery file, now when u run the code it will start blinking questionmark and explanatory mark , where as it should show tickbox. can anyone please tell me what could be the reason for this error. thanks in advance