body { 
    text-align: center; 
    font: 20px Helvetica, sans-serif; 
}
h1 { 
  font-size: 50px; 
  margin-top: 1rem;
}
.main article {
    display: block; 
    margin: 0 auto;  
}
.main img {
    width: 50%;
    max-width:500px;
}
@media screen and (max-width: 768px) {
    .main img {
        width: 100%;
    }
}