body {
  background: rgb(204,204,204); 
}
page {
  background: white;
  display: block;
  margin: 0 auto;
  margin-top: 50px;
  margin-bottom: 50px;
  box-shadow: 0 0 0.5cm rgba(0,0,0,0.5);
  width: 70%;
  min-height: 500px;
}

@media screen and (max-width: 900px) {
  page {
    width: 100%;
    margin:0;
  }
}