JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
  Here is some content!
  <div class="shadow" id="shadowLeft"></div>
</div>

CSS

#container{
    width: 100px;
    height: 100px;
    margin: 50px;
    border: 1px solid pink;
    position:relative;
}
.shadow{
    position:absolute;
    height: 100%;
    width: 4px;
    left:0px;
    top:0px;
    box-shadow: -4px 0 3px black;
}