JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">header</div>
<div id="splashbox">splashbox</div>
<div id="content">content</div>
<div id="sidebar">sidebar</div>
<div id="footer">footer</div>

CSS

#header {
    width: 100%;
    background: #222;
    height: 50px;
    display: block;
}

#splashbox {
    width: 100%;
    background: linear-gradient(#444,#ccc);
    height: 80px;
    display: block;
}

#content {
    background: #fff;
    display: block;
    width: 80%;
    height: 200px;
    float: left;
}

#sidebar {
    background: #333;
    width: 20%;
    height: 200px;
    float:right;
    display: block;
}

#footer {
width: 100%;
    height: 100px;
    display: block;
    background: #ccc;
}