JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    width: 100px;
    height: 30px;
    background: #369;
    margin: 100px auto;
    position: relative;
}
div:before {
    content: "";
    position: absolute;
    top: 100%;
    left: 0;
    border: 10px solid transparent;
    border-right: 40px solid #369;
    border-top: 2px solid #369;
}
div:after {
    content: "";
    position: absolute;
    top: 100%;
    right: 0;
    border: 10px solid transparent;
    border-left: 40px solid #369;
    border-top: 2px solid #369;
}