JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper"></div>
<div id="header"><div>stuff</div></div><div id="shadow">&nbsp;</div><div id="main"><div>stuff</div></div>
<div id="wrapper"></div>

CSS

#wrapper{
    background: #FFFFFF;
    height: 20px;
    position: relative;
    width: 100%;
    z-index: 20;
}
#shadow{
    width: 0px;
    box-shadow: 1px 0px 5px 2px #005377;
    position: relative;
}
#header, #main ,#shadow{
    background: #fff;
    display:inline-block;
    height: 70px;
}
#header{
    position: relative;  
    background: #FFFFFF;
    z-index:5;
}
#header, #main { 
    width: 49%;
}