.hero {
  background:
    linear-gradient(90deg, #020307f2 0%, #020307b8 48%, #02030742 100%),
    url("images/observatory.jpg") center/cover;
}

.stars { opacity: .18; }
.orb { opacity: .58; }

.session-grid .image {
  position: relative;
  overflow: hidden;
  background:
    linear-gradient(#07101b44, #020307e8),
    url("images/night-sky.jpg") center/cover;
}

.session-grid .image > *:not(.moon) { position: relative; }
.session-grid .image .moon { display: none; }

.observatory {
  background:
    linear-gradient(90deg, #05070de8, #08101ca8),
    url("images/stars.jpg") center/cover;
}

.finale {
  background:
    linear-gradient(#05081266, #020307e0),
    url("images/night-sky.jpg") center/cover;
}

@media (max-width: 760px) {
  .hero { background-position: 62% center; }
  .orb { opacity: .35; }
}