#back-to-top {
    font-size: 20px;
    position: fixed;
    bottom: 40px;
    right: 40px;
    z-index: 9999;
    width: 40px;
    height: 40px;
    text-align: center;
    line-height: 35px;
    background: #036;
    color: #FC3;
    cursor: pointer;
    border: 0;
    border-radius: 2px;
    text-decoration: none;
    transition: opacity 0.2s ease-out;
    opacity: 0;
}
#back-to-top:hover {
    background: #FC3;
    color: #036;
}
#back-to-top.show {
    opacity: 1;
}