#myBtn {
    display: none;
    position: fixed;
    bottom: 20px;
    right: 30px;
    z-index: 99;
    font-size: 18px;
    border: none;
    outline: none;
    /*background-color: red;*/
    /*color: white;*/
    cursor: pointer;
    padding: 15px;
    border-radius: 4px;
}

    #myBtn:hover {
        background-color: #555;
    }