JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bg">
<div class="borderleft"></div>
<div class="borderright"></div> 
</div>

CSS

.borderright {
    line-height: 0%;
    width: 0;
    border-top: 50px solid transparent;
    border-right: 400px solid white;
    position: absolute;
    bottom: 0;
    right: 0;
}
.borderleft {
    line-height: 0%;
    width: 0;
    border-top: 50px solid transparent;
    border-left: 400px solid white;
    position: absolute;
    bottom: 0;
    left: 0;
}
.bg {
    background-color: black;
    position: relative;
    width: 100%;
    height: 400px;
}