JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.header {
    background: #000;
    width:1100px;
    height:150px;
    margin:auto;
    border:1px solid rgba(0, 0, 0, 0);
    -webkit-border-bottom-right-radius: 10px;
    -webkit-border-bottom-left-radius: 10px;
    -moz-border-radius-bottomright: 10px;
    -moz-border-radius-bottomleft: 10px;
    border-bottom-right-radius: 10px;
    border-bottom-left-radius: 10px;
    z-index:2;
}

.headeron {
    border:0px solid #000;
    background-color:#FFF;
    width:1080;
    height:100px;
    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    border-radius: 10px;
    z-index:5000;
    margin-top: 10px;        
}