Source: Divi support.

1. Give the item the class custom-scroll
2. Add this to a code module. The 500 is the number of pixels from the top where it starts to fade out.

<style>
.custom-scroll {
    opacity: 1;
    transition:opacity 1s;
}
.custom-scroll.custom-hide {
    opacity: 0;
}
</style>
<script>
jQuery(function($){
$(function() {
    var header = $(".custom-scroll");
    $(window).scroll(function() {
        var scroll = $(window).scrollTop();

        if (scroll >= 500) {
            header.addClass("custom-hide");
        } else {
            header.removeClass("custom-hide");
        }
    });
});
});	
</script>Code language: HTML, XML (xml)