.sfondo {
  margin: 0;
  background-image: url(https://static.vecteezy.com/ti/vettori-gratis/p3/16829862-vettore-illustrazione-di-graffiti-sfondo-senza-soluzione-di-continuita-graffiti-arte-textures-nel-un-disegnato-a-mano-stile-vecchio-scuola-e-urbano-strada-arte-tema-per-maglietta-disegno-tessile-sfondo-sfondo-e-stampe-vettoriale.jpg);
  background-attachment: fixed;
  background-repeat: no-repeat;
  background-size: cover;
}

.riquadro {
  background-color: #000;
  color: #fff;
  border-radius: 10px;
  padding: 15px;
  text-align: center;
  margin: 50px auto; 
  font-size: 25px;
   flex: 1; 
  min-width: 200px; 
  border: 2px solid orange;
  opacity: 0.9; 
 
}
 
body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; 
  font-size: 14px;
  color: #000;
  margin: 0;
  padding: 0;
  background: #eee; 
}

h1, p {
  font-size: 20px; 
  font-family: Helvetica, Arial, sans-serif; 
  text-align: center;
  color: white;
}

footer{
  background-color: black;
  text-align:center;
  font-size:12px;
  color: white;
  border-top: 1px solid orange;
  opacity:90%;
  }