html {
    scroll-behavior: smooth;
}

.scrolltopsmooth-btn {
    z-index: 9999;
    position: fixed;
    bottom: 15px;
    width: 45px;
    height: 45px;
    line-height: 1;
    border-radius: 50%;
    overflow: hidden;
    cursor: pointer;
    padding: 14px 0px 15px 15px;
}