body {
  background-color: black;
}
#contenidor1 {
  border-style: solid;
  border-color: red;
  background-image: url(media/pebble-light.jpg);
  min-width: 640px;
  max-width: 1024px;
  margin-right: auto;
  margin-left: auto;
  padding-right: 10px;
  padding-left: 10px;
}