JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#top" id="top-button">Top</a>

CSS

#top-button {
    background-color: rgba(0, 0, 0, 0.5);
    
    border-radius: 3px;
    
    color: #00A2E8;
    
    display: none;
    
    padding: 5px;
    
    position: fixed;
    top: 35px;
    right: 35px;
    
    text-decoration: none;
}

JavaScript

var i = 0;

for ( ; i < 100; i++ )
    {
        document.body.innerHTML += "<p>Hello</p>"
    }

$(window).bind('scroll', function () {
    if (window.scrollY > 100) {
        $('#top-button').fadeIn(300);
    } else {
        $('#top-button').fadeOut(300);
    }
});