.scroll-top {
    width: 40px;
    height: 40px;
    line-height: 40px;
    position: fixed;
    top: 100%;
    right: 50px;
    font-size: 16px;
    border-radius: 4px;
    z-index: 99;
    text-align: center;
    cursor: pointer;
    -webkit-transition: 1s ease;
    transition: 1s ease;
    border: none;
}

.scroll-top.open {
    top: 90%;
}