section {
  background-image: url("http://media.istockphoto.com/photos/mature-man-walking-dog-in-frosty-landscape-picture-id473423242?s=2048x2048");
  background-repeat: no-repeat;
  position: relative;
  width: 100%;
  height: 100vh;
  margin-left: auto;
  margin-right: auto;
  background-position: center center;
  display: table;
}

.jumbotron {
  background-color: transparent;
  display: table-cell;
  vertical-align: middle;
  text-align: center;
}