JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bar-long"></div>

CSS

.bar-long {
    height: 5px;
    background-color: #009ACF;
    width: 0px;
    z-index: 1000;
    position: fixed;
    top: 50px;
    left: 0;
}

body {
    height:3000px;   
}

JavaScript

$(window).scroll(function() {

    // calculate the percentage the user has scrolled down the page
    var scrollPercent = 100 * $(window).scrollTop() / ($(document).height() - $(window).height());

    $('.bar-long').css('width', scrollPercent +"%"  );

});