JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header">
			</div>

CSS

.header {
	position: fixed;
	top: 0;
	left: 0;
	right: 0;
	background-color: #000;
	height: 110px;
	}
.header:after {
    content: '';
    background-color: red;
    position: absolute;
    display: block;
    width: 100px;
    top: 110px;
    left: 50%;
    margin-left: -50px;
    height: 50px;
    border-radius: 0 0 50px 50px;
}