JSFiddle - React, Tailwind, and code Playground

HTML

<div class="trapezium"></div>

CSS

.trapezium {
    border-bottom: 80px solid #fff;
    border-left: 45px solid transparent;
    border-right: 45px solid transparent;
    padding: 0 8px 0 0;
    height: 0;
    width: 120px;
    position: relative;
    margin: 2em auto;
}

.trapezium:before {
    border-bottom: 90px solid #000;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    padding: 0 8px 0 0;
    height: 0;
    width: 130px;
    position: absolute;
    bottom: -85px;
    left: -55px;
    content: "";
    z-index: -1;
}