html {
    background: #BBB;
}

body {
    font: normal 16px "Segoe UI", Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
}

.contenido {
    background-color: white;
    border-radius: 10px;
    padding: 20px;
    width: 88%;
}