JSFiddle - React, Tailwind, and code Playground

HTML

<body class="ui-layout">
    <header id="site-header">
        <section id="user-plate">
        </section>
    </header>
    <nav id="site-menu">
    </nav>
    <div id="site-content">
        <section>
        </section>
    </div>
    <footer></footer>
</body>

CSS

#site-header {
    background-color: #465660;
    height: 120px;
    
}
#site-header #user-plate {
    width: 1024px;
    min-width: 1024px;
    margin: 0 auto;
    height: 120px;
    position: relative;
}

#site-menu {
    background-color: #fff;
    height: 64px;
    position: absolute;
    top: 100px;
    display: block;
    width: 1024px;
}

#site-content {
    background-color: #eee;
    min-height: 500px;
}