<!-- backgroud to gray -->
<div class="slds-backdrop slds-backdrop--open"></div>
<!-- modal to pop-up -->
<div role="dialog" tabindex="-1" aria-labelledby="commentBg" class="slds-modal slds-fade-in-open ">
  <div class="slds-modal__container">
    <div class="slds-modal__content slds-p-around--small">
      <!-- body -->
    </div>
  </div>
</div>