JSFiddle - React, Tailwind, and code Playground

HTML

<div id="fixed">
je ne scrolle pas
</div>
<div id="screen">
</div>

CSS

#screen { 
height: 2000px;
}
#fixed {
  width: 200px;
  height:80px;
  border: solid 1px green;
}
.fixme {
  position: fixed;
  top: 50px; 
  left: 50px;
}

JavaScript

$(function(){

for (i=0;i<100;i++){
$('#screen').append($('<p/>').html('ligne '+i))
}
$(window).on('scroll', function(){

 if ($(window).scrollTop()>100){
 $('#fixed').addClass('fixme')
 }
 else{
 $('#fixed').removeClass('fixme')
 }

})

})