#totop_btn {
    position: fixed;
    right: 25px;
    bottom: 100px;

    width: 40px;
    height: 40px;
    z-index: 9;

    background-color: #000000;
    border: 1px solid #fff;

    transition: all 0.15s ease-in;
    visibility: hidden;
    opacity: 0;
}
#totop_btn.active {
    opacity: 1;
    visibility: visible;
}
#totop_btn.active:hover, #totop_btn.active:active {
    background-color: #262626;
}