JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.header {
  position: relative;
  height: 70px;
  width: 100%;
  background: #d3d3d3;
}

.header:before {
        content: "";
        display: block;
        position: absolute;
        border-radius: 0 0% 0% 100%;
        width: 3%;
    height: 70px;
    background-color: #fff;
    right: 0;
    top: 0;
}

.header:after {
        content: "";
        display: block;
        position: absolute;
        border-radius: 0% 0% 100% 0%;
        width: 3%;
    height: 70px;
    background-color: #fff;
    left: 0;
    top: 0;
}