[Dilettante_Pro]

<style>
.call_button {
   position:fixed;
   opacity:1;
   transition-property:opacity;
   transition-duration: 1s;

}
.scroll {
   opacity:0;
}
</style>

<button class="call_button">Call!</button>
<div style="height:400px;width:300px">Lorem ipsum dolor sit amet, consectetur adipisicing elit. A alias atque, autem consectetur corporis dicta dolor doloremque dolores ducimus ea inventore laboriosam libero nam officia possimus quos tempore tenetur voluptatum!</div>

<script>
var but = document.querySelector('.call_button');

window.onscroll = function() {
      but.classList.add('scroll');
      setTimeout("but.classList.remove('scroll');",1000)
}
</script>