.botao-topo {
    position: fixed;
    right: 20px;
    bottom: 20px;
    z-index: 999;
    display: none;
    padding: 0.8rem 1rem;
    border: 1px solid #444;
    background: #fff;
    color: #111;
    cursor: pointer;
    font: inherit;
}

.botao-topo.visivel {
    display: block;
}