JSFiddle - React, Tailwind, and code Playground

HTML

<div class="blackbox"></div>

CSS

body{
   height:800px;
}

.blackbox{
background:black;
width:100%;
height:50px;
top:0;
overflow:hidden;
position:fixed;
display:none;
z-index:3;
}

JavaScript

$(document).ready(function(){
    $(window).scroll(function () {
       $('.blackbox').fadeIn();
        if($(this).scrollTop()==0){
         $('.blackbox').fadeOut();
        }
    });
});