.principal {
    /* The image used */
    background-image: linear-gradient(rgba(0, 0, 20, 0.4), rgba(0, 0, 20, 0.4)), url("img/table.png");

    min-height: 80vh;
  
    /* Center and scale the image nicely */
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
    /* background-attachment: fixed; */
}