#back-to-top {
    height: 40px;
    width: 40px;
    position: fixed;
    right: 0;
    z-index: 99;
    border-radius: 50%;
    box-shadow: 0px 0px 5px #ccc;
    margin: 17px;
	background-color:#999999;
    bottom: -150px;
    opacity: 0;
    transition: all .5s ease;
}
#back-to-top.show-btt {
    bottom: 0;
    opacity: 1;
    transition: all .5s ease;
}