.hero-background {
  background-image: url('img/background/london_675x1080.jpg');
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
}

@media (min-width: 640px) {
  .hero-background {
    background-image: url('img/background/london_1024x576.jpg');
  }
}

@media (min-width: 1024px) {
  .hero-background {
    background-image: url('img/background/london_1920x1080.jpg');
  }
}