$(document).scroll(function () {
s_top = $("body").scrollTop();
yes = $("#id").offset().top;
if(s_top > yes){
$('.btn-my').addClass('fixed-btn');
} else {
$('.btn-my').removeClass('fixed-btn');
}
if ($(window).scrollTop() == $(document).height() - $(window).height()) {
$('.btn-my').removeClass('fixed-btn');
$('.btn-my').addClass('fixed-btn-bottom');
} else {
$('.btn-my').removeClass('fixed-btn-bottom');
}
});<div class="desktops fotorama">@media screen and (max-width: 760px) {
.desktops.fotorama {display:block!important;}
.fotorama__noise......
}
.desktops.fotorama {display:none;}