JSFiddle - React, Tailwind, and code Playground

HTML

<div id="footer">
</div>

CSS

#footer{
    width:500px;
    height:100px;
    margin:50px auto;
    background-color:black;   
}


#footer:after{
    border-bottom: 30px solid black;
    border-left: 500px solid transparent;
    height: 0;
    width: 0;
    top:20px;
    content:"";
    position:absolute;
 }

#footer:before{
    border-bottom: 40px solid grey;
    border-left: 500px solid transparent;
    height: 0;
    width: 0;
    top:10px;
    content:"";
    position:absolute;
 }