JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div id="content">
        This is some content
    </div>
</div>

CSS

.container {
    text-align: right;
    width: 400px;
}
#content {
    width: 10px;
    height:20px;
    background-color:red;
    overflow: hidden;
    float:right;
}

JavaScript

var width;

$('#content').click(function(){
    if($(this).hasClass('open')){
        $(this).removeClass('open');
        width = "10px";
    } else {
        $(this).addClass('open');
        width = "300px";
    }
    $(this).animate({
        width: width
      }, 200, function() {
      });
    
});