Appear after scroll depth

scroll.css

#rum_sst_tab {
    opacity: 0;
    transition: all .5s;
    visibility: hidden;
}

#rum_sst_tab.show {
    opacity: 1;
    visibility: visible;
}

scroll.js

$(document).scroll(function () {
    var y = $(this).scrollTop();
    var scrollHeight = 500;//Set the number to your desired distance from the top
    if (y > scrollHeight) {
        $("#rum_sst_tab").addClass("show");
    } else {
        $('#rum_sst_tab').removeClass("show");
    }

});