:root{
    --night-1:#0b1233;
    --night-2:#1b2556;
    --night-3:#3a1a56;
    --horizon-1:#6d1e3f;
    --horizon-2:#a43e2a;
    --aurora-mint:#8de16a;
    --aurora-green:#47cf73;
    --aurora-teal:#2fb69d;
    --aurora-yellow:#efe08e;
  }

  html,body{
    height:100%;
    margin:0;
    background:#000;
    overflow:hidden;
  }

  .sky{
    position:fixed; inset:0;
    background:
      radial-gradient(1200px 800px at 80% 85%, rgba(255,170,120,.25), transparent 60%),
      linear-gradient(to top,
        var(--horizon-2) 0%,
        var(--horizon-1) 12%,
        #6b1d7a 24%,
        var(--night-3) 46%,
        var(--night-2) 72%,
        var(--night-1) 100%);
  }

  .aurora{
    position:absolute; inset:0;
    mix-blend-mode:screen;
  }

  .band{
    position:absolute;
    width:160vmax; height:60vmax;
    left:-20vmax; top:40%;
    opacity:.6;
    filter:blur(22px) saturate(120%);
    animation: drift 60s ease-in-out infinite alternate;
  }

  .b1{
    background:linear-gradient(90deg,
      transparent 12%,
      rgba(71,207,115,.8) 38%,
      rgba(141,225,106,.8) 50%,
      rgba(47,182,157,.8) 62%,
      transparent 88%);
    animation-duration:12s;
  }
  .b2{
    background:linear-gradient(90deg,
      transparent 10%,
      rgba(239,224,142,.8) 45%,
      rgba(141,225,106,.8) 56%,
      rgba(71,207,115,.8) 66%,
      transparent 90%);
    top:75%;
    transform:rotate(-10deg);
    animation-duration:11s;
    animation-delay:-3s;
  }
  .b3{
    background:linear-gradient(90deg,
      transparent 18%,
      rgba(47,182,157,.7) 50%,
      rgba(141,225,106,.75) 62%,
      rgba(239,224,142,.7) 74%,
      transparent 82%);
    top:30%;
    transform:rotate(6deg);
    animation-duration:14s;
    animation-delay:-6s;
  }

  @keyframes drift {
    0% {
      transform: translateX(-12vmax) translateY(-6vmax) rotate(var(--r, -8deg));
    }
    50% {
      transform: translateX(6vmax) translateY(2vmax) rotate(var(--r, -5deg));
    }
    100% {
      transform: translateX(12vmax) translateY(-4vmax) rotate(var(--r, -8deg));
    }
  }