JSFiddle - React, Tailwind, and code Playground

HTML

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex optio officia, repellendus placeat eligendi earum, aliquid deleniti culpa nobis officiis modi.</p>

<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Qui accusamus cupiditate iusto eum odit mollitia vero reprehenderit, ex...

CSS

.btn-scroll {
  cursor: pointer;
  position: fixed;
  display: block;
  bottom: 35px;
  right: 20px;
  overflow: hidden;
  width: 44px;
  height: 44px;
  z-index: 999;
  background-color: #68bec4;
  border: none;
  text-align: center;
  border-radius: 50%;
  transition: 0.3s background-color;
}
.hide {
  display: none;
}

JavaScript

$(document).ready(function() {
	$btn = $('.btn-scroll');
  
	$(window).scroll(function(){
		var $height = $(this).scrollTop();
		var maxheight = 300;
		if($height > maxheight) {
			$btn.removeClass('hide');
		} else {
    	$btn.addClass('hide');
		}
	});

   $btn.on('click', function() {
     $('html, body').animate({
       scrollTop: 0
     }, '300');
   });

 });