JSFiddle - React, Tailwind, and code Playground

HTML

<div id="supra-top-wrap">
    <div id="top-wrap">
        <nav id="main-nav">
            <ul>
                <li><a href="#" title="Naar het forum">Forum</a></li>
                <li><a href="#" title="Naar het contactformulier">Contact</a></li>
                <li><a href="#" title="Bekijk de sitemap">Sitemap</a></li>
                <li><a href="#" title="Hier adverteren?">Adverteren</a></li>
             </ul>
        </nav>
    </div>
    <!-- /END TOP-WRAP -->
    
    <nav id="sub-nav">
        <ul>
            <li><a href="#" title="Alles van 'webdesign' bekijken">Webdesign</a></li>
            <li><a href="#" title="Alles van 'forum' bekijken">SEO</a></li>
            <li><a href="#" title="Alles van 'tutorials' bekijken">Tutorials</a></li>
            <li><a href="#" title="Alles van 'webhosting' bekijken">Webhosting</a></li>
        </ul>
    </nav>
    <!-- /END SUB-NAV -->
</div>

<div id="content">
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi. Nulla quis sem at nibh elementum imperdiet. Duis sagittis ipsum. Praesent mauris. Fusce nec tellus sed augue semper porta. Mauris massa. Vestibulum lacinia arcu eget nulla. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. </p>

<p>Curabitur sodales ligula in libero. Sed dignissim lacinia nunc. Curabitur tortor. Pellentesque nibh. Aenean quam. In scelerisque sem at dolor. Maecenas mattis. Sed convallis tristique sem. Proin ut ligula vel nunc egestas porttitor. Morbi lectus risus, iaculis vel, suscipit quis, luctus non, massa. Fusce ac turpis quis ligula lacinia aliquet. Mauris ipsum. </p>

<p>Nulla metus metus, ullamcorper vel, tincidunt sed, euismod in, nibh. Quisque volutpat condimentum velit. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Nam nec ante. Sed lacinia, urna non tincidunt mattis, tortor neque adipiscing diam, a cursus...

CSS

div#top-wrap {
    width: 100%;
    height: 43px;
    background: #0073bf;
    z-index: 10;
    position: relative;
}

/* main nav */
nav#main-nav {
    width: 960px;
    margin: 0 auto;
    height: 100%;
}

nav#main-nav > ul {
    list-style: none;
    overflow: hidden;
    height: 100%;
    float: left;
}

nav#main-nav > ul li {
    float: left;
    padding-top: 11px;
    height: 100%;
}

nav#main-nav > ul li:after {
    content: "";
    height: 80%;
    width: 1px;
    margin: 0 1em;
    border-right: 1px solid white;
}

nav#main-nav > ul li:last-child::after {border: none 0;} 

nav#main-nav > ul li a, nav#sub-nav ul li a {
    text-decoration: none;
    color: white;
    font-weight: bold;
    font-family: "Segoe UI";
}

nav#main-nav > ul li a:hover, nav#sub-nav ul li a:hover, input#search-button:hover {text-decoration: underline;}

/* sub-nav */
nav#sub-nav {
    width: 345px;
    height: 38px;
    margin: 0 auto;
    padding: 0 0.8em 0.2em;
    position: relative;
    border: 1px solid #efefef;
    border-top: 0;
    background: white;
}

nav#sub-nav:hover {box-shadow: 0 0 8px rgba(0,0,0,0.12);}

nav#sub-nav ul {
    overflow: hidden;
    height: 100%;
    list-style: none;
}

nav#sub-nav ul li {
    float: left;
    padding-top: 8px;
    height: 100%;
    margin-right: 0.8em;
}

nav#sub-nav ul li:last-child {margin-right: 0;}

nav#sub-nav ul li a {color: #666;}
nav#sub-nav ul li a:hover {
    color: #aaa;
    text-decoration: none;
}

/* supra-top-wrapper */
div#supra-top-wrap {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 100;
}

/* content */
div#content {
    width: 80%;
    margin: 100px auto;
}
div#content p {
    line-height: 1.4;
    margin-bottom: 1.2em;
}

JavaScript

$(window).scroll(function(){
    
    if( $(window).scrollTop() > 0 ) {

        $('#top-wrap').animate({ top: -38 }, 400);
        $('#sub-nav').animate({ top: -70 }, 400);

    }
    else if( $('#top-wrap').offset().top !== 0 ) {

        $('#top-wrap').stop(true).animate({ top: 0 }, 400, function() {
            $('#sub-nav').stop(true).animate({ top: 0 }, 400); 
        });

    }

});