Answers for "show a class that is hidden"

hide a div

<div id="main"> 
  <p> Hide/show this div </p>
</div>

('#main').hide(); //to hide

// 2nd way, by injecting css using jquery
$("#main").css("display", "none");

is display-block a class

<span class="d-block p-2 bg-primary text-white">d-block</span>
<span class="d-block p-2 bg-dark text-white">d-block</span>