JSFiddle - React, Tailwind, and code Playground

by Alexandru Gatea

HTML

<div class="container">
  <div class="box"></div>
</div>
<div class="dummy"></div>

CSS

* {
  margin: 0;
}

.container {
  width: 100%;
  height: 100vh;
  background: #eee;
  position: relative;
}

.box {
  width: 100px;
  height: 100px;
  background: red;
  opacity: 1;
  position: absolute;
  bottom: 0;
}

.dummy {
  height: 300vh;
}

JavaScript

var container = $('.container').height();

$(window).on("scroll", function(){
	scroll = $(window).scrollTop();
  var stp = (scroll * 100) / container;
	$('.box').css('opacity', (100 - stp) / 100);
});