.outer {
     /* The image used */
  background-image: url("https://www.mariapaschalidou.com/images/03_Semiotics_of_the_PhantasmaMaria_Paschalidou_2014.jpg");

  /* Full height */
  height: 100%; 

  /* Center and scale the image nicely */
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;

}