#myBtn {
    position: fixed;
    bottom: 35px;
    right: 35px;
    z-index: 99;
    border: 2px solid black;
    outline: none;
    color: black;
    cursor: pointer;
    padding: 15px;
    border-radius: 5px;
    transition: all 500ms;
}

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