Transparent Glowing Border: CSS Border Animation

Transparent Glowing Border

A glowing border with nothing inside it: the halo spills both ways while two pools of light circle the ring. The glow is a blurred wrapper around a masked conic ring, so the middle stays clear.

Also known as: glowing border css, glowing border transparent background, glow border no background, css glowing outline.

No background needed

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-transparent-glow-border">
  <span class="bdr-transparent-glow-border-glow" aria-hidden="true"></span>
  <span class="bdr-transparent-glow-border-ring" aria-hidden="true"></span>
  No background needed
</div>

CSS

@property --bdr-transparent-glow-border-a {
  syntax: "<angle>";
  inherits: true;
  initial-value: 0deg;
}
.bdr-transparent-glow-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;
  --hot: color-mix(in oklch, var(--c), #22d3ee 45%);
  --ring: conic-gradient(from var(--bdr-transparent-glow-border-a), var(--c), var(--hot) 22%, var(--c) 45%, color-mix(in srgb, var(--c) 35%, transparent) 50%, var(--c) 55%, var(--hot) 72%, var(--c) 95%);
  animation: bdr-transparent-glow-border-turn 6s linear infinite;
}
.bdr-transparent-glow-border-glow,
.bdr-transparent-glow-border-ring,
.bdr-transparent-glow-border-glow::before {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  pointer-events: none;
}
.bdr-transparent-glow-border-glow {
  filter: blur(0.55em);
  animation: bdr-transparent-glow-border-breathe 3s cubic-bezier(0.45, 0, 0.55, 1) infinite;
}
.bdr-transparent-glow-border-glow::before {
  content: "";
  padding: 0.3em;
  background: var(--ring);
  -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);
}
.bdr-transparent-glow-border-ring {
  padding: 0.12em;
  background: var(--ring);
  -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);
}
@keyframes bdr-transparent-glow-border-turn {
  to { --bdr-transparent-glow-border-a: 360deg; }
}
@keyframes bdr-transparent-glow-border-breathe {
  0%, 100% { opacity: 0.95; }
  50%      { opacity: 0.5; }
}
@media (prefers-reduced-motion: reduce) {
  .bdr-transparent-glow-border,
  .bdr-transparent-glow-border-glow { animation: none; }
}

@media (prefers-reduced-motion: reduce) {
  .bdr-transparent-glow-border, .bdr-transparent-glow-border *, .bdr-transparent-glow-border::before, .bdr-transparent-glow-border::after, .bdr-transparent-glow-border *::before, .bdr-transparent-glow-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.

Transparent Glowing Border

HTML

CSS

Customizing this snippet

Similar border animations