JSFiddle - React, Tailwind, and code Playground

HTML

<html><body><h1></h1></body></html>

CSS

body.fail { background:red; }
body.pass { background: green; }
h1        { position: fixed; }

JavaScript

$(function() {
    var $window = $( window ), $body = $( document.body );
    $body.height( $window.height() * 2 );

    $window
        .scrollTop( $window.height() )
        .scroll();

    var passfail = ( 0 === $window.scrollTop() ) ? 'fail' : 'pass';

    $body
        .addClass( passfail )
        .find( 'h1' )
        .text( passfail );
})