JSFiddle - React, Tailwind, and code Playground

HTML

<div class="upper-container">
    Hidden container
</div>
<div class="main-container">
    Visibile container
    <div class="click-this">
        Click This to Slide Down
    </div>
</div>

CSS

.upper-container{
  position:reltive;
  width:100%;
  padding-top:0px;
  background:red;
  height:0px;  
  overflow:hidden;
}
.main-container{
    background: blue;
      position: relative;    
}
.click-this{
    background: #fff;
    color: #333;
    padding: 20px;
    margin-left: 20px;
    width: 300px;
    margin-top: 40px;
}

JavaScript

$(document).ready(function(){
    var heightVar = 0 - $(window).height();
    $('.main-container').css('height', $(window).height()+'px');
    $('.click-this').on('click', function(){
        $('.upper-container').animate({height: '100px', paddingTop: '40px'}, 500);
    });
});