mask layer

<style>
    #BgDiv{
        width:100%;
        height:100%;
        background-color: rgba(0,0,0,0.05);
        opacity: 0.3;

    }
</style>

<div id="BgDiv" style="display: none;"></div>

Close button plus class .click-close-hide 
click display button #newQuestionBtn and #addTable

<script> 
   // The mask layer is displayed and hidden 
   // Click to add to make the mask layer appear 
   $('body').on('click','#addTable',function(){ 
       $('#BgDiv').show (); 
       $('#BgDiv').css("z-index","1000"); 
   })

    //Click on the new question to make the mask layer appear and hide the added pop-up box 
   $('body').on('click','#newQuestionBtn',function(){ 
       $('#BgDiv').show (); 
        $('#BgDiv').css("z-index","1000"); 
       $('.modal-dialog.modal-lg .modal-content ').hide(); 
   }) 
  $( 'body').on('click','.click-close-hide',function(){ 
         $('#BgDiv').hide(); 
          $('.modal-dialog.modal-lg .modal- content ').show(); 
         $('#BgDiv').css("z-index","-1"); 
     }) 
   </script>