body {
    font-family: Arial, sans-serif;
    text-align: center;
    margin: 50px;
    position: relative;
    overflow: hidden;
}
input, button {
    font-size: 16px;
    padding: 10px;
    margin: 10px;
    z-index: 1;
    position: relative;
}
.fondo {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    z-index: -1;
}
#result {
    font-size: 20px;
    font-weight: bold;
}