Aurora Border: CSS Border Animation

Aurora Border

Green, teal and violet light drifts along the inside of a dark frame like the northern lights. Two conic layers turn at different speeds under a blur, with a crisp copy masked to the rim.

Also known as: aurora gradient border, blurred gradient border css, northern lights border.

Aurora

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-aurora-border"><span class="bdr-aurora-border-rim"></span>Aurora</div>

CSS

@property --bdr-aurora-border-a {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}
@property --bdr-aurora-border-b {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}
.bdr-aurora-border {
  --c: var(--bdr-color, #3b82f6);
  font-size: var(--bdr-size, 16px);
  position: relative;
  display: grid;
  place-items: center;
  width: 15em;
  height: 8.5em;
  border-radius: 1em;
  font-family: system-ui, sans-serif;
  font-weight: 600;
  --night: color-mix(in srgb, var(--c) 8%, #050914);
  --aurora:
    conic-gradient(from var(--bdr-aurora-border-a) at 30% 50%, #34d399, transparent 18% 40%, var(--c) 55%, transparent 70% 85%, #34d399),
    conic-gradient(from var(--bdr-aurora-border-b) at 70% 50%, #a78bfa, transparent 20% 45%, #22d3ee 60%, transparent 75% 90%, #a78bfa);
  isolation: isolate;
  overflow: hidden;
  background: var(--night);
  color: #e2e8f0;
  letter-spacing: 0.04em;
  animation:
    bdr-aurora-border-a 9s linear infinite,
    bdr-aurora-border-b 13s linear infinite reverse;
}
.bdr-aurora-border::before,
.bdr-aurora-border::after {
  content: "";
  position: absolute;
  pointer-events: none;
}
.bdr-aurora-border::before {
  inset: 0;
  z-index: -2;
  background: var(--aurora);
  filter: blur(1.1em);
}
.bdr-aurora-border::after {
  inset: 1.1em 1.3em;
  z-index: -1;
  border-radius: 1em;
  background: var(--night);
  filter: blur(0.9em);
}
.bdr-aurora-border-rim {
  position: absolute;
  inset: 0;
  padding: 0.1em;
  border-radius: inherit;
  background: var(--aurora);
  -webkit-mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  -webkit-mask-composite: xor;
  mask: linear-gradient(#000 0 0) content-box exclude, linear-gradient(#000 0 0);
  pointer-events: none;
}
@keyframes bdr-aurora-border-a {
  to { --bdr-aurora-border-a: 360deg; }
}
@keyframes bdr-aurora-border-b {
  to { --bdr-aurora-border-b: 360deg; }
}

@media (prefers-reduced-motion: reduce) {
  .bdr-aurora-border, .bdr-aurora-border *, .bdr-aurora-border::before, .bdr-aurora-border::after, .bdr-aurora-border *::before, .bdr-aurora-border *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

Customizing this snippet

Color: set --bdr-color on the element or a parent. Currently previewing #3b82f6.
Base size: set --bdr-size. Every other dimension is in em, so the whole thing scales together. Currently previewing 16px.
Speed: change the duration on the transition or animation shorthand. Staggered delays are relative, so they keep their rhythm.
Reduced motion: the rule at the end of the CSS turns the motion off for people who asked their OS for less of it. Keep it.

Aurora Border

HTML

CSS

Customizing this snippet

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