html { 
  background: url(15.jpg) no-repeat center center fixed; 
 -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover
}


h1{color: white;
font-size: 20px;
margin-top: 10%;
margin-left: 45% }

.piętnaście{color: white;
margin-top: 15%;
margin-left: 90% }