JSFiddle - React, Tailwind, and code Playground

HTML

<div id="foo">
</div>
<div id="nav">
</div>
<div id="bar">
</div>

CSS

#foo{
    height:100px;
    width:100%;
}
#bar{
    height:1000px;
    width:100%;
}

#nav{
    width: 80%;
    height: 100px;
    margin: 0 auto;
    background-color: #FFCC00;
}
.fixed-nav{
    position: fixed;
    top: 0;
}

JavaScript

var bottom = $('#nav').offset().top;
$(window).scroll(function(){    
    if ($(this).scrollTop() > bottom){ 
        $('#nav').addClass('fixed-nav'); 
    }
    else{
        $('#nav').removeClass('fixed-nav');
    }
});