:root{
  --orb-size: 80px;
}

body, html {
  height: 100%;
  margin: 0;
}

.bg{
  /* Full height */
  height: 100%; 

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

.orb{
  position: absolute;
  margin-left: auto;
  margin-right: auto;
  bottom: 10%;
  left: 50%;
  height: var(--orb-size);
  width: var(--orb-size);
  transform: translateX(calc(var(--orb-size) * -0.75));
}

@media only screen and (max-device-width: 800px){
  :root{
    --orb-size: 160px;
  }
  .orb{
    bottom: 15%;
  }
}