body {
    background: url(../mantenimiento/fondo.jpg);
    background-repeat: no-repeat;
    background-size: auto 100vh;
    background-position: top;
}
h2 {
    font-family:Arial, Helvetica, sans-serif;
    text-align: center;
    font-size: 20px;
    color: #555555;
    padding: 10px 0px;
    margin: auto;
    padding: 20px;
}
p {
    font-family:Arial, Helvetica, sans-serif;
    text-align: center;
    font-size: 14px;
    color: #555555;
    padding: 10px 0px;
    margin: auto;
    padding: 20px; 
}
.cajaimagen {
    width: 100%;
    text-align: center;
    
}
.imagen {
    width: 100%;
    max-width: 450px;
    margin: 20px auto;
}