JSFiddle - React, Tailwind, and code Playground

HTML

<span id=mybutton>TUTAJ, NA DOLE PO PRAWEJ</span>
AAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AAAAAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAA
<br><br><br><br>
AAAAAV<br>AAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AA<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AAr>AAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AA<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AAr>AAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AA
AAAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAAAAA
<br><br><br><br>
AAAAAV<bAAAA
<br><br><br><br>
AAAAAV<br><br><br>
AA<br>AAAA
<br>AAr><br><br>
AA<br>AAAA
<br>AA<br>AAAA
<br>AA

CSS

#mybutton {
   position: fixed;
   bottom:0;
   right:0;
   z-index:2;
   opacity: 0.0;
   visibility: visible;
   color:red;
   cursor: pointer;    
}

JavaScript

var isVisible = false;


$(window).scroll(function(){
     var shouldBeVisible = $(window).scrollTop()>200;
	 if (shouldBeVisible && !isVisible) {
		  isVisible = true;
		  $('#mybutton').css({opacity: 0.0, visibility: "visible"}).animate({opacity: 1.0});
	 } else if (isVisible && !shouldBeVisible) {
		  isVisible = false;
		  $('#mybutton').css({opacity: 1.0, visibility: "visible"}).animate({opacity: 0.0});;
	}
});