#scrollTopBtn{
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 45px;
    height: 45px;
    background: #ffffff;
    color: #000000;
    font-size: 20px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;

    opacity: 0;
    visibility: hidden;
    transition: 0.3s;

    box-shadow: 0 5px 15px rgba(0,0,0,0.2);
    z-index: 999;
}

#scrollTopBtn:hover{
    background: #ff0000;
    color: #fff;
}

#scrollTopBtn.show{
    opacity:1;
    visibility:visible;
}